avplay: Always free find_stream_info options

CC: libav-stable@libav.org
Bug-Id: CID 1238794
avplay: Always free opts

CC: libav-stable@libav.org
Bug-Id: CID 733793
avprobe: Remove a pointless check

The element is always valid.

CC: libav-stable@libav.org
Bug-Id: CID 732276
avconv: fix leak in filter error

CC: libav-stable@libav.org
Bug-Id: CID 1005311
avconv: check return value

CC: libav-stable@libav.org
Bug-Id: CID 1224275
avformat: Make avformat_free_context handle NULL

Work as the other free()-like functions.

Bug-Id: CID 1087081
CC: libav-stable@libav.org
cmdutils: Use the correct guard

The OptionDef arrays are terminated with a { NULL } element not NULL.

CC: libav-stable@libav.org
Bug-Id: CID 703769