WPrefs: fix icon position preview lagging one click behind

The posV widget was moved/resized but the parent frame (posVF) was
never redrawn, so the visual update only appeared on the next event
that triggered a redraw. Add WMRedisplayWidget after the move.

WPrefs.app/Icons.c

@@ -141,6 +141,8 @@ static void showIconLayout(WMWidget * widget, void *data)
 		WMMoveWidget(panel->posV, panel->icon_position.width - 2 - w, panel->icon_position.height - 2 - h);
 		break;
 	}
+
+	WMRedisplayWidget(panel->posVF);
 }
 
 static void minipreview_slider_changed(WMWidget *w, void *data)