Better buffer-overrun prevention

fixes end-of-buffer detection. Adds buffer-was-empty detection.

Bug: 204445255
Test: ran poc from bug
Change-Id: I42117ce1455d1cac2bd43f16d67d77ec436b0fe2
(cherry picked from commit b51ed962d5186b68f883540e557894e881a8272d)
(cherry picked from commit 190e90959f3c34781c5276d50a5ee561c438db09)
Merged-In:I42117ce1455d1cac2bd43f16d67d77ec436b0fe2
1 file changed