keyboard: defer position-changed till we have a rect

Emitting it that soon results in JS warnings, as we don't have
everything in place yet. The position-changed signal will be
emitted from other locations as soon as we have it.

https://gitlab.gnome.org/GNOME/gnome-shell/issues/464

Closes: #464

js/ui/keyboard.js

@@ -526,9 +526,7 @@ var FocusTracker = new Lang.Class({
         this._currentWindow = window;
         if (window) {
             this._currentWindowPositionId = this._currentWindow.connect('position-changed', () => {
-                if (global.display.get_grab_op() == Meta.GrabOp.NONE)
-                    this.emit('position-changed');
-                else
+                if (global.display.get_grab_op() != Meta.GrabOp.NONE)
                     this.emit('reset');
             });
         }