(Hopefully) prevent NPE

app/src/main/java/net/i2p/android/router/I2PActivityBase.java

@@ -52,7 +52,6 @@ public abstract class I2PActivityBase extends ActionBarActivity implements
     /**
      * Router variables
      */
-    protected String _myDir;
     protected boolean _isBound;
     protected boolean _triedBind;
     protected ServiceConnection _connection;
@@ -95,7 +94,6 @@ public abstract class I2PActivityBase extends ActionBarActivity implements
         Util.d(this + " onCreate called");
         super.onCreate(savedInstanceState);
         _sharedPrefs = getSharedPreferences(SHARED_PREFS, 0);
-        _myDir = getFilesDir().getAbsolutePath();
 
         // If the Activity wants to use a ViewPager, provide it.
         // If the Activity can make use of two panes (if available),

app/src/main/java/net/i2p/android/router/MainActivity.java

@@ -301,7 +301,7 @@ public class MainActivity extends I2PActivityBase implements
             setPref(PREF_AUTO_START, true);
             svc.manualStart();
         } else {
-            (new File(_myDir, "wrapper.log")).delete();
+            (new File(Util.getFileDir(this), "wrapper.log")).delete();
             startRouter();
         }
     }