avcodec/jpeg2000dec: fix near null pointer dereference

Fixes Ticket2840

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/jpeg2000dec.c

@@ -1343,6 +1343,7 @@ static void jpeg2000_dec_cleanup(Jpeg2000DecoderContext *s)
 {
     int tileno, compno;
     for (tileno = 0; tileno < s->numXtiles * s->numYtiles; tileno++) {
+        if (s->tile[tileno].comp) {
             for (compno = 0; compno < s->ncomponents; compno++) {
                 Jpeg2000Component *comp     = s->tile[tileno].comp   + compno;
                 Jpeg2000CodingStyle *codsty = s->tile[tileno].codsty + compno;
@@ -1351,6 +1352,7 @@ static void jpeg2000_dec_cleanup(Jpeg2000DecoderContext *s)
             }
             av_freep(&s->tile[tileno].comp);
         }
+    }
     av_freep(&s->tile);
     s->numXtiles = s->numYtiles = 0;
 }