minor refactoring and signalling panel subtitle by node change

Fixes issue where Footage Viewer subtitle wouldn't update when
dropping footage in.

app/widget/viewer/viewersizer.cpp

@@ -101,9 +101,10 @@ void ViewerSizer::UpdateSize()
     return;
   }
 
-  // If the aspect ratio is 0, the widget is always hidden
+  // If the aspect ratio is 0, default to taking all space
   if (!width_ || !height_) {
-    widget_->setVisible(false);
+    widget_->move(0, 0);
+    widget_->resize(width(), height());
     return;
   }
 
@@ -142,7 +143,6 @@ void ViewerSizer::UpdateSize()
   }
 
   // Size widget to the UI space we've calculated
-  widget_->setVisible(true);
   widget_->resize(available_width, available_height);
 
   // Adjust to aspect ratio