Fix race bug in attemptIncStrong

The compensating onLastStrongRef call could be made even when there
was no onIncStrongAttempted call to compensate for.  This
happened in the OBJECT_LIFETIME_STRONG case when e.g. curCount
was initially zero, but was concurrently incremented by another
thread.

I believe the old code was also incorrect in the
curCount = INITIAL_STRONG_VALUE + 1 case,
which seems to be possible under unlikely conditions.
In that case, I believe the compensating call IS needed.
Thus the condition was also changed.

Bug: 30503444
Change-Id: I44bcbcbb1264e4b52b6d3750dc39b041c4140381