avfilter: check filter link validity

Remove now redundant check.

CC: libav-stable@libav.org
Bug-Id: CID 700371
audiointerleave: check av_new_packet return value

CC: libav-stable@libav.org
Bug-Id: CID 1087078
img2dec: check av_new_packet return value

CC: libav-stable@libav.org
Bug-Id: CID 1087077
flac_picture: prevent a possible out of bound write

At "mimetype[len] = 0;" mimetype is a 64 element array and len might be
equal to or greater than that.

CC: libav-stable@libav.org
Bug-Id: CID 1061055
lavf: replace rename() with ff_rename()

The new function wraps errno so that its value is correctly reported
when other functions overwrite it (eg. in case of logging).

CC: libav-stable@libav.org
Bug-Id: CID 1135748
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
matroskadec: fix leak on error

CC: libav-stable@libav.org
Bug-Id: CID 1026767
matroskadec: check return values

CC: libav-stable@libav.org
Bug-Id: CID 733712
matroskaenc: check avio_open_dyn_buf return value

CC: libav-stable@libav.org
Bug-Id: CID 703629
mxfdec: add missing break

CC: libav-stable@libav.org
Bug-Id: CID 732232
mxfenc: Fix possible integer overflows

None of these are likely unless the user is writing a file with two billion
streams or a duration of around two months.

CC: libav-stable@libav.org
Bug-Id: CID 700568 / CID 700569 / CID 700570 /
        CID 700571 / CID 700572 / CID 700573
mov: fix assigment check

CC: libav-stable@libav.org
Bug-Id: CID 1197050