Add de265_push_end_of_frame function.

Indicates that de265_push_data has just received data until the end of a frame.
All data pending at the decoder input will be pushed into the decoder and
the decoded picture is pushed to the output queue.
Merge pull request #73 from Vincit/master

Add de265_push_end_of_frame function.
fix access to unavailable reference picture in broken streams