jpeg2000: Initialize code blocks structures in precincts to 0

Prevent use of uninitialized memory / valgrind failure.

Found-by: ubitux
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

libavcodec/jpeg2000.c

@@ -416,7 +416,7 @@ int ff_jpeg2000_init_component(Jpeg2000Component *comp,
                 if (!prec->zerobits)
                     return AVERROR(ENOMEM);
 
-                prec->cblk = av_malloc_array(prec->nb_codeblocks_width *
+                prec->cblk = av_mallocz_array(prec->nb_codeblocks_width *
                                               prec->nb_codeblocks_height,
                                               sizeof(*prec->cblk));
                 if (!prec->cblk)