ff_v4l2_m2m_create_context initialized V4L2m2mContext.fd to 0
which is a valid file descriptor value. Next ff_v4l2_m2m_codec_init
failed and v4l2_m2m_destroy_context closed file descriptor 0 even
though it didn't belong to V4L2m2mContext.
Signed-off-by: Pavel Koshevoy <pkoshevoy@gmail.com>