Harden reading settings file to prevent startup freeze

There is an uncommon issue where settings file becomes corrupted and results in exception during iniParser.ReadFile(). This will cause game to freeze at startup on either a black screen or splash. Users can resolve by deleting settings.ini to restore defaults, but this usually requires community support.
This commit hardens settings impot in the following ways:
1. Create a settings backup file once successfully read.
2. Add exception handling for iniParser.ReadFile() to recover from corrupted settings file.
3. First fallback is to backup settings file.
4. Second fallback is to restore defaults automatically. This isn't ideal, but better than game freezing.
Currently unknown what causes settings.ini to become corrupted in this way. The repro sample provided by a user was filled with 5kb of "NULL" characters.

Assets/Scripts/SettingsManager.cs

@@ -33,6 +33,7 @@ public class SettingsManager
     {
         const string defaultsIniName = "defaults.ini";
         const string settingsIniName = "settings.ini";
+        const string settingsBakExt = ".bak";
         const string settingsDistIniName = "settings-{0}.ini";
 
         const string sectionDaggerfall = "Daggerfall";
@@ -718,15 +719,21 @@ public void SaveSettings()
 
         #region Private Methods
 
-        string SettingsName()
+        string SettingsName(bool isBackup = false)
         {
+            string name;
             if (string.IsNullOrEmpty(DistributionSuffix))
-                return settingsIniName;
+                name = settingsIniName;
             else
-                return string.Format(settingsDistIniName, DistributionSuffix);
+                name = string.Format(settingsDistIniName, DistributionSuffix);
+
+            if (isBackup)
+                name = Path.ChangeExtension(name, settingsBakExt);
+
+            return name;
         }
 
-        void ReadSettingsFile()
+        void CreateDefaultSettingsFile(string userIniPath)
         {
             // Load defaults.ini
             TextAsset asset = Resources.Load<TextAsset>(defaultsIniName);
@@ -735,43 +742,65 @@ void ReadSettingsFile()
             defaultIniData = iniParser.ReadData(reader);
             reader.Close();
 
+            // Create file
+            File.WriteAllBytes(userIniPath, asset.bytes);
+
+            Debug.LogFormat("Creating new '{0}' at path '{1}'", SettingsName(), userIniPath);
+        }
+
+        void ReadSettingsFile()
+        {
             // Must have settings.ini in persistent data path
-            string message;
             string userIniPath = Path.Combine(PersistentDataPath, SettingsName());
             if (!File.Exists(userIniPath))
+                CreateDefaultSettingsFile(userIniPath);
+
+            // Load settings.ini and try to handle exception
+            // Failing to load settings at this stage might cause game to freeze at startup
+            // First try backup from last good startup then fallback to defaults
+            try
+            {
+                userIniData = iniParser.ReadFile(userIniPath);
+            }
+            catch (Exception)
             {
-                // Create file
-                message = string.Format("Creating new '{0}' at path '{1}'", SettingsName(), userIniPath);
-                File.WriteAllBytes(userIniPath, asset.bytes);
-                DaggerfallUnity.LogMessage(message);
+                Debug.Log("Error parsing settings.ini. Trying backup file.");
+                string userIniBakPath = Path.Combine(PersistentDataPath, SettingsName(true));
+                try
+                {
+                    userIniData = iniParser.ReadFile(userIniBakPath);
+                }
+                catch(Exception)
+                {
+                    Debug.Log("Error parsing settings backup. Restoring defaults.");
+                    CreateDefaultSettingsFile(userIniPath);
+                    userIniData = iniParser.ReadFile(userIniPath);
+                }
             }
 
             // Log ini path in use
-            message = string.Format("Using '{0}' at path '{1}'", SettingsName(), userIniPath);
-            DaggerfallUnity.LogMessage(message);
+            Debug.LogFormat("Using '{0}' at path '{1}'", SettingsName(), userIniPath);
 
-            // Load settings.ini or set as read-only
-            userIniData = iniParser.ReadFile(userIniPath);
+            // Create a backup after successfully parsing ini data
+            WriteSettingsFile(true);
 
             // Ensure user ini data in sync with default ini data
             SyncIniData();
         }
 
-        void WriteSettingsFile()
+        void WriteSettingsFile(bool isBackup = false)
         {
+            string name = SettingsName(isBackup);
             if (iniParser != null)
             {
                 try
                 {
-                    string path = Path.Combine(PersistentDataPath, SettingsName());
-                    if (File.Exists(path))
-                    {
-                        iniParser.WriteFile(path, userIniData);
-                    }
+                    string path = Path.Combine(PersistentDataPath, name);
+                    iniParser.WriteFile(path, userIniData);
                 }
                 catch
                 {
-                    DaggerfallUnity.LogMessage("Failed to write settings.ini.");
+                    Debug.LogFormat("Failed to write {0}", name);
                 }
             }
         }