xwayland/wm: TYPE_WM_NORMAL_HINTS xcb value buffer overread when starting LibreOffice

Found by ASan (AddressSanitizer). I added a log statement:

--- a/xwayland/window-manager.c
+++ b/xwayland/window-manager.c
@@ -616,6 +616,11 @@ weston_wm_window_read_properties(struct weston_wm_window *window)
 				}
 			break;
 		case TYPE_WM_NORMAL_HINTS:
+			if (xcb_get_property_value_length(reply) < sizeof window->size_hints) {
+				weston_log("TYPE_WM_NORMAL_HINTS is too short: %d < %d\n",
+						xcb_get_property_value_length(reply), sizeof window->size_hints);
+				break;
+			};
 			memcpy(&window->size_hints,
 			       xcb_get_property_value(reply),
 			       sizeof window->size_hints);

Happens only when launching LibreOffice (built with GTK3) under Xwayland (GDK_BACKEND=x11 soffice):

[14:16:06.178] TYPE_WM_NORMAL_HINTS is too short: 60 < 72
[14:16:06.182] TYPE_WM_NORMAL_HINTS is too short: 60 < 72

Doesn't seem to cause any actual problems, but still weird...

P.S. looking forward to merge requests being enabled here :)