[scenario] trigger firstFrameLatch on exception. (#50981)

If we hit this exception (which we seem to do a lot), then we weren't triggering the first frame latch.

testing/scenario_app/android/app/src/main/java/dev/flutter/scenarios/ExternalTextureFlutterActivity.java

@@ -418,7 +418,6 @@ private void onImageAvailable(ImageReader reader) {
         // Simply log and return.
         Log.i(TAG, "Surface disconnected from ImageWriter", e);
         image.close();
-        return;
       }
 
       Log.v(TAG, "Output image");