Themes: Fix native crash in libandroidfw

If a missing attribute needs to be added in somewhere in the middle
of the bag, a segfault would occur because we change curEntry to a
value that is beyond the set's allocated space.  This patch stores
curEntry in prevEntry before changing it's value and memmove uses
prevEntry to index the set.

Change-Id: Ie70f2ad465097c3acf76caa729999c424fb01ee2