Improved JavaScript TTS initialization process

Fixed a problem that null may be passed
as an argument when initializing JavaScriptTTS.
Changed to refer to context from within the class
instead of the argument when initializing JavaScriptTTS.

Author: mikunimaru

AnkiDroid/src/main/java/com/ichi2/anki/AbstractFlashcardViewer.java

@@ -393,7 +393,7 @@ public abstract class AbstractFlashcardViewer extends NavigationDrawerActivity i
     private boolean mFocusTypeAnswer;
 
     /** Text to speech */
-    private JavaScriptTTS mTalker = new JavaScriptTTS(AbstractFlashcardViewer.this);
+    private JavaScriptTTS mTalker = new JavaScriptTTS();
 
     // ----------------------------------------------------------------------------
     // LISTENERS

AnkiDroid/src/main/java/com/ichi2/anki/JavaScriptTTS.java

@@ -38,8 +38,9 @@ public class JavaScriptTTS implements TextToSpeech.OnInitListener {
     private static boolean mTtsOk;
     private static final Bundle mTtsParams = new Bundle();
 
-    JavaScriptTTS(Context context) {
-        mTts = new TextToSpeech(context, this);
+    JavaScriptTTS() {
+        Context mContext = AnkiDroidApp.getInstance().getApplicationContext();
+        mTts = new TextToSpeech(mContext, this);
     }
 
     /** OnInitListener method to receive the TTS engine status */