avcodec/jpeg2000dec: Skip DWT if nothing is coded

Improves speed in uncommon case

Fixes: Timeout
Fixes: 10964/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_JPEG2000_fuzzer-5132066034286592

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/jpeg2000dec.c

@@ -1597,7 +1597,7 @@ static int decode_cblk(Jpeg2000DecoderContext *s, Jpeg2000CodingStyle *codsty,
                cblk->data + cblk->length - 2*(term_cnt < cblk->nb_terminations) - t1->mqc.bp);
     }
 
-    return 0;
+    return 1;
 }
 
 /* TODO: Verify dequantization for lossless case
@@ -1694,6 +1694,7 @@ static inline void tile_codeblocks(Jpeg2000DecoderContext *s, Jpeg2000Tile *tile
     for (compno = 0; compno < s->ncomponents; compno++) {
         Jpeg2000Component *comp     = tile->comp + compno;
         Jpeg2000CodingStyle *codsty = tile->codsty + compno;
+        int coded = 0;
 
         t1.stride = (1<<codsty->log2_cblk_width) + 2;
 
@@ -1723,11 +1724,12 @@ static inline void tile_codeblocks(Jpeg2000DecoderContext *s, Jpeg2000Tile *tile
                          cblkno++) {
                         int x, y;
                         Jpeg2000Cblk *cblk = prec->cblk + cblkno;
-                        decode_cblk(s, codsty, &t1, cblk,
+                        int ret = decode_cblk(s, codsty, &t1, cblk,
                                     cblk->coord[0][1] - cblk->coord[0][0],
                                     cblk->coord[1][1] - cblk->coord[1][0],
                                     bandpos);
-
+                        if (ret)
+                            coded = 1;
                         x = cblk->coord[0][0] - band->coord[0][0];
                         y = cblk->coord[1][0] - band->coord[1][0];
 
@@ -1743,7 +1745,9 @@ static inline void tile_codeblocks(Jpeg2000DecoderContext *s, Jpeg2000Tile *tile
         } /* end reslevel */
 
         /* inverse DWT */
-        ff_dwt_decode(&comp->dwt, codsty->transform == FF_DWT97 ? (void*)comp->f_data : (void*)comp->i_data);
+        if (coded)
+            ff_dwt_decode(&comp->dwt, codsty->transform == FF_DWT97 ? (void*)comp->f_data : (void*)comp->i_data);
+
     } /*end comp */
 }