NPE for new Equalizer feature

1. Open the equlizer
2. Check the button
3. Change the vertical bars
4. Close the dialogFragment (with out saving or reseting)
5. Now ,save dialog will appear just close it with out pressing save or don't save buttons (with back button or touching out of it)
6. NPE here https://code.videolan.org/videolan/vlc-android/blob/881bf973aeecdcf285d59e0702dab95863c9bc7d/vlc-android/src/org/videolan/vlc/gui/audio/EqualizerFragment.java#L524 because button is checked and mService is null.