add comment to explain the last commit

pd/nw/pdgui.js

@@ -3024,6 +3024,9 @@ function gui_image_configure(cid, tag, image_key, tk_anchor) {
 
 // Move an image
 function gui_image_coords(cid, tag, x, y) {
+    // ggee/image accepts a message that can trigger this, meaning
+    // [loadbang] can end up calling this before the patchwindow exists.
+    // So we have to check for existence below
     if (patchwin[cid]) {
         elem_move(get_gobj(cid, tag), x, y);
     }