Android: Don't rely on onPause for pausing before destroying surface

Fixes a crash which was uncovered (or just made more likely?)
by the previous commit.

Source/Android/app/src/main/java/org/dolphinemu/dolphinemu/fragments/EmulationFragment.java

@@ -186,6 +186,7 @@ public final class EmulationFragment extends Fragment implements SurfaceHolder.C
   {
     Log.debug("[EmulationFragment] Surface destroyed.");
     NativeLibrary.SurfaceDestroyed();
+    mRunWhenSurfaceIsValid = true;
   }
 
   public void stopEmulation()