fraps: check for overread.

Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavcodec/fraps.c

@@ -111,6 +111,10 @@ static int fraps2_decode_plane(FrapsContext *s, uint8_t *dst, int stride, int w,
              */
             if(j) dst[i] += dst[i - stride];
             else if(Uoff) dst[i] += 0x80;
+            if (get_bits_left(&gb) < 0) {
+                free_vlc(&vlc);
+                return AVERROR_INVALIDDATA;
+            }
         }
         dst += stride;
     }