tsdemux: Fix flags comparison operator precedence

Fix operator precedence, so the whole operation is
negated instead of only flags variable.

https://bugzilla.gnome.org/show_bug.cgi?id=722096

gst/mpegtsdemux/pesparse.c

@@ -328,7 +328,7 @@ mpegts_parse_pes_header (const guint8 * data, gsize length, PESHeader * res)
   }
 
   /* jump if we don't have a PES 2nd extension */
-  if (!flags & 0x01)
+  if (!(flags & 0x01))
     goto stuffing_byte;
 
   /* Extension flag 2 */