inputMethod: Check that there is an existing cursor location

Commit 17d9ec5788 made the input method call update() more eagerly,
but also at times that it does not have a cursor position yet. Make
it bail out correctly in that situation.

Fixes: 17d9ec5788 ("inputMethod: Keep Capabilite.FOCUS before context.focus_in/focus_out")
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2876>

js/misc/inputMethod.js

@@ -380,9 +380,11 @@ export const InputMethod = GObject.registerClass({
             return;
         this._updateCapabilities();
         this._context.set_content_type(this._purpose, this._hints);
+        if (this._cursorRect) {
             this._context.set_cursor_location(
                 this._cursorRect.x, this._cursorRect.y,
                 this._cursorRect.width, this._cursorRect.height);
+        }
         this._emitRequestSurrounding();
     }
 });