Fix android fragment lifecycle

Fix for blocking call to `graphics.onDestroy()`. Currently still leads to a crash in some situations, but I could use some help trying to figure out the root cause. Please don't merge without testing. Continuation of https://github.com/libgdx/libgdx/pull/1439

On my Intel emulator this crashes now with the following logcat output;

````
F/libc    ( 3642): Fatal signal 11 (SIGSEGV) at 0x00000e4a (code=1), thread 3657 (Thread-114)
I/DEBUG   (  921): *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
I/DEBUG   (  921): Build fingerprint: 'generic_x86/google_sdk_x86/generic_x86:4.4.2/KK/1082983:eng/test-keys'
I/DEBUG   (  921): Revision: '0'
I/DEBUG   (  921): pid: 3642, tid: 3657, name: Thread-114  >>> io.blueapps.android <<<
I/DEBUG   (  921): signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 00000e4a
````
I'm not sure what this could be caused by. I will investigate further tomorrow.