Handler null check for when AndroidNotifier is closed (#4131)

[Zhuinden]

Fixes #4131 which occurs when async queries are not yet finished, but Realm instance is closed.

[Zhuinden]

I don't think I've signed the contributor license agreement thing yet, though.

[zaki50]

@Zhuinden Can you add a test case to reproduce #4131?

[cmelchior]

Hi @Zhuinden . Thanks a ton for this. Can you also add a changelog entry?

[Zhuinden]

I'm trying to run library tests in general but I kinda got stuck with it ¬¬

com.getkeepsafe.relinker.MissingLibraryException: lib/unknown/librealm-jni.so
at com.getkeepsafe.relinker.ApkLibraryInstaller.installLibrary(ApkLibraryInstaller.java:85)
at com.getkeepsafe.relinker.ReLinkerInstance.loadLibraryInternal(ReLinkerInstance.java:180)
at com.getkeepsafe.relinker.ReLinkerInstance.loadLibrary(ReLinkerInstance.java:136)
at com.getkeepsafe.relinker.ReLinker.loadLibrary(ReLinker.java:70)
at com.getkeepsafe.relinker.ReLinker.loadLibrary(ReLinker.java:57)
at io.realm.internal.RealmCore.loadLibrary(RealmCore.java:59)
at io.realm.Realm.init(Realm.java:187)

I added a changelog entry, but I ran out of time on trying to add tests for now.

I can give a sample project that produces this errors though: https://github.com/Zhuinden/realm-error-4131

The errors occur when you press BACK or you rotate the screen.

[Zhuinden]

I think #3834 will handle this