jpeg2000dec: check that we have enough components for MCT

Fixes out of array accesses

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/jpeg2000dec.c

@@ -325,6 +325,11 @@ static int get_cod(Jpeg2000DecoderContext *s, Jpeg2000CodingStyle *c,
     tmp.nlayers = bytestream2_get_be16u(&s->g);
     tmp.mct     = bytestream2_get_byteu(&s->g); // multiple component transformation
 
+    if (tmp.mct && s->ncomponents < 3) {
+        av_log(s->avctx, "MCT %d with too few components (%d)\n", tmp.mct, s->ncomponents);
+        return AVERROR_INVALIDDATA;
+    }
+
     if ((ret = get_cox(s, &tmp)) < 0)
         return ret;