codecparsers: h264parser: guard against ref_pic_markings overflow

Part-of: <!1704>

gst-libs/gst/codecparsers/gsth264parser.c

@@ -723,13 +723,17 @@ gst_h264_slice_parse_dec_ref_pic_marking (GstH264SliceHdr * slice,
 
       dec_ref_pic_m->n_ref_pic_marking = 0;
       while (1) {
-        refpicmarking =
-            &dec_ref_pic_m->ref_pic_marking[dec_ref_pic_m->n_ref_pic_marking];
-
         READ_UE (nr, mem_mgmt_ctrl_op);
         if (mem_mgmt_ctrl_op == 0)
           break;
 
+        if (dec_ref_pic_m->n_ref_pic_marking >=
+            G_N_ELEMENTS (dec_ref_pic_m->ref_pic_marking))
+          goto error;
+
+        refpicmarking =
+            &dec_ref_pic_m->ref_pic_marking[dec_ref_pic_m->n_ref_pic_marking];
+
         refpicmarking->memory_management_control_operation = mem_mgmt_ctrl_op;
 
         if (mem_mgmt_ctrl_op == 1 || mem_mgmt_ctrl_op == 3)