4xmdec: test version for cfrms, fix out of array accesses

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

libavcodec/4xm.c

@@ -811,6 +811,11 @@ static int decode_frame(AVCodecContext *avctx, void *data,
             return AVERROR_INVALIDDATA;
         }
 
+        if (f->version <= 1) {
+            av_log(f->avctx, AV_LOG_ERROR, "cfrm in version %d\n", f->version);
+            return AVERROR_INVALIDDATA;
+        }
+
         for (i = 0; i < CFRAME_BUFFER_COUNT; i++)
             if (f->cfrm[i].id && f->cfrm[i].id < avctx->frame_number)
                 av_log(f->avctx, AV_LOG_ERROR, "lost c frame %d\n",