avcodec/g2meet: Check tile_width in epic_jb_decode_tile()

Fixes: out of array access
Fixes: 21469/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_G2M_fuzzer-5199357982015488

Alternatively the arrays can be made bigger or the index can be clipped.
In case a real file with such huge tiles exist we ask the user to upload it.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 5501bb28)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/g2meet.c

@@ -917,6 +917,11 @@ static int epic_jb_decode_tile(G2MContext *c, int tile_x, int tile_y,
     awidth      = FFALIGN(tile_width,  16);
     aheight     = FFALIGN(tile_height, 16);
 
+    if (tile_width > (1 << FF_ARRAY_ELEMS(c->ec.prev_row_rung))) {
+        avpriv_request_sample(avctx, "large tile width");
+        return AVERROR_INVALIDDATA;
+    }
+
     if (els_dsize) {
         int ret, i, j, k;
         uint8_t tr_r, tr_g, tr_b, *buf;