Improve handling of invalid frames.

The code was not checking for frame sizes smaller than 3 bytes, and the
 partition size checks might have failed if the input buffer was within
 16MB of the top of the heap.
In addition, the reference count on the current frame buffer was not
 being decremented on error, so after a small number of errors, no new
 frame buffer could be found and it would run off the list of them.

Change-Id: I0c60dba6adb1e2a29df39754f72a56ab6c776b46