avcodec/jpeg2000dec: Assert that pixel format descriptor is not NULL

We only look up pixel formats from a fixed list so none should ever
fail to be found

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/jpeg2000dec.c

@@ -171,6 +171,8 @@ static int pix_fmt_match(enum AVPixelFormat pix_fmt, int components,
     int match = 1;
     const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(pix_fmt);
 
+    av_assert2(desc);
+
     if (desc->nb_components != components) {
         return 0;
     }