[droidvdec] don't try to create codec data if we do not have any. Fixes JB#29724
[droidvdec] don't try to create codec data if we do not have any. Fixes JB#29724

This can happen with MPEG4 video muxed in AVI container. We do not get any codec_data
from avidemux yet we try to map the NULL bufffer and return an error.

mlehtima/gst-droid,sailfishos/gst-droid,mlehtima/gst-droid