We would return true when opening assets in read/write mode despite
the fact that the files are not writable. The logic now matches
that of the qrc file engine.
This also adds a unit test for Android-specific issues.
[ChangeLog][Android][Important Behavior Changes] Opening assets with
QIODevice::ReadWrite now returns false to correctly indicate that the
files are not writable.
Change-Id: I019cc27861fc9b000dc13c5e0a38c0fc09a08671
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@theqtcompany.com>
Reviewed-by: Christian Stromme <christian.stromme@theqtcompany.com>
Reviewed-by: BogDan Vatra <bogdan@kde.org>
