Fix startup window size on XOrg

The window size was restored too early which caused the window to be a little bigger then it should on each launch. Restore window size after that window was mapped.

src/app.js

@@ -30,6 +30,8 @@ class ClapperApp extends AppBase
         window.add_css_class('nobackground');
         window.set_child(clapperWidget);
         window.set_titlebar(dummyHeaderbar);
+
+        this.mapSignal = window.connect('map', this._onWindowMap.bind(this));
     }
 
     vfunc_open(files, hint)
@@ -39,4 +41,12 @@ class ClapperApp extends AppBase
         this._openFiles(files);
         this.activate();
     }
+
+    _onWindowMap(window)
+    {
+        window.disconnect(this.mapSignal);
+        this.mapSignal = null;
+
+        window.child._onWindowMap(window);
+    }
 });