Use readFile for declarations too

This let's the loader survive whenever the watched file gets removed.

index.ts

@@ -141,6 +141,16 @@ function findConfigFile(compiler: typeof typescript, searchPath: string, configF
     return undefined;
 }
 
+function readFile(fileName) {
+    fileName = path.normalize(fileName);
+    try {
+        return fs.readFileSync(fileName, {encoding: 'utf8'})
+    }
+    catch (e) {
+        return;
+    }
+}
+
 // The loader is executed once for each file seen by webpack. However, we need to keep
 // a persistent instance of TypeScript that contains all of the files in the program
 // along with definition files and options. This function either creates an instance
@@ -326,16 +336,6 @@ function ensureTypeScriptInstance(loaderOptions: LoaderOptions, loader: any): {
     // make a (sync) resolver that follows webpack's rules
     let resolver = makeResolver(loader.options);
 
-    var readFile = function(fileName) {
-        fileName = path.normalize(fileName);
-        try {
-            return fs.readFileSync(fileName, {encoding: 'utf8'})
-        }
-        catch (e) {
-            return;
-        }
-    }
-
     var moduleResolutionHost = {
         fileExists: (fileName: string) => readFile(fileName) !== undefined,
         readFile: (fileName: string) => readFile(fileName)
@@ -516,7 +516,7 @@ function ensureTypeScriptInstance(loaderOptions: LoaderOptions, loader: any): {
                 filePath = path.normalize(filePath);
                 var file = instance.files[filePath];
                 if (file) {
-                    file.text = fs.readFileSync(filePath, {encoding: 'utf8'});
+                    file.text = readFile(fileName) || '';
                     file.version++;
                     instance.version++;
                 }