librtmp: append the correct field to the string

Also prevent a NULL pointer dereference.

CC: libav-stable@libav.org
Bug-Id: CID 1250329 / CID 1250331
libvpxenc: clean memory on error

CC: libav-stable@libav.org
Bug-Id: CID 733795
lavc: fix bitshifts amount bigger than the type

CC: libav-stable@libav.org
Bug-Id: CID 1194387 / CID 1194389 / CID 1194393 / CID 1206638
mov: check ff_get_wav_header() return value

CC: libav-stable@libav.org
Bug-Id: CID 717497