Fix Error When Input Buffer is Full

In cases where the input buffer is exhausted and the picture has still
not been decoded fully, the multi-thread decoder would read beyond the
allocated size.

Bug: 38328132
Test: asan-enabled POC before/after patch on master.
Change-Id: I8a73b819558407c130dcafeeab1a9bff77688dfc
(cherry picked from commit 86bfec8d3215dbdabbe79dba128628976ebfc6ef)