[Android] Fixes #2679 - Crash resuming from screen off

Before destroying the static Java-side data, wait for the SDL native thread,
*and* the listener thread that waits on it to trigger a clean up.

android-project/src/org/libsdl/app/SDLActivity.java

@@ -932,16 +932,16 @@ class SDLSurface extends SurfaceView implements SurfaceHolder.Callback,
             // This is the entry point to the C app.
             // Start up the C app thread and enable sensor input for the first time
 
-            SDLActivity.mSDLThread = new Thread(new SDLMain(), "SDLThread");
+            final Thread sdlThread = new Thread(new SDLMain(), "SDLThread");
             enableSensor(Sensor.TYPE_ACCELEROMETER, true);
-            SDLActivity.mSDLThread.start();
+            sdlThread.start();
             
             // Set up a listener thread to catch when the native thread ends
-            new Thread(new Runnable(){
+            SDLActivity.mSDLThread = new Thread(new Runnable(){
                 @Override
                 public void run(){
                     try {
-                        SDLActivity.mSDLThread.join();
+                        sdlThread.join();
                     }
                     catch(Exception e){}
                     finally{ 
@@ -951,7 +951,8 @@ class SDLSurface extends SurfaceView implements SurfaceHolder.Callback,
                         }
                     }
                 }
-            }).start();
+            });
+            SDLActivity.mSDLThread.start();
         }
     }