Do not use default setting when value is false

fix brave#4903

Auditors: @bbondy

Test Plan:
1. Turn on/off "Always show the URL bar" in about:preferences#general
2. The title mode should work as expected

js/settings.js

@@ -60,7 +60,7 @@ const resolveValue = (settingKey, settingsCollection) => {
 
 module.exports.getSetting = (settingKey, settingsCollection) => {
   const setting = resolveValue(settingKey, settingsCollection)
-  if (setting) return setting
+  if (typeof setting !== 'undefined') return setting
   return getDefaultSetting(settingKey, settingsCollection)
 }