demux: ts: fix uninitialized fields (fix #15319)

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/demux/mpeg/ts.c

@@ -4500,7 +4500,7 @@ static void PMTSetupEsDvbSubtitle( demux_t *p_demux, ts_pes_t *p_pes,
             }
             else
             {
-                p_subs_es = malloc( sizeof(*p_subs_es) );
+                p_subs_es = calloc( 1, sizeof(*p_subs_es) );
                 if( !p_subs_es )
                     break;