SurfaceTexture: fix a bug with buffer reallocation

This change fixes an issue involving buffer reallocation and the
ALLOW_DEQUEUE_CURRENT_BUFFER mode in SurfaceTexture.  The bug happened
when the buffer slot currently attached to the GL texture was selected
for dequeuing, but the dequeue operation caused the buffer to be
reallocated.  Because the buffer is new, the image producer could fill
the buffer and queue it before an updateTexImage call, which would
result in the "slot %d is current" error in queueBuffer.

Bug: 5631630
Change-Id: Icdd8bc5cad3c7db43953446d9be2603aaea11a8d