This occurs for video codecs that have codec_tag set, but are are not listed
in ff_codec_bmp_tags (e.g. AV_CODEC_ID_BINKAUDIO, AV_CODEC_ID_IFF_ILBM).

Fixes ticket #3269.
Signed-off-by: Peter Ross <pross@xvid.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>