With cli usage the decoder might have not set the colorspace during
encoder init, manual colorspace override might be needed in such
cases.
Signed-off-by: Anton Khirnov <anton@khirnov.net>

This applies commit 5de64bb3 (the source of the above commit message)
to libutvideoenc as well.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>