Fix a couple of minor publicly-reported GC bugs.

An assertion was incorrectly assigning rather than testing, and
there was the usual buggy attempt to recover from failure rather
than just aborting in the HeapSource.cpp dvmHeapSourceStartup.
(The Copying.cpp dvmHeapSourceStartup by contrast will just
segfault if an allocation fails, but that's fine too.)

Bug: https://code.google.com/p/android/issues/detail?id=61562
Bug: https://code.google.com/p/android/issues/detail?id=61563
Change-Id: I237a6f923a07d61709f99ab67c9a18dbc7e6c839