renderer: don't render window on other mons during anim in

fixes #5139

src/Window.hpp

@@ -296,6 +296,7 @@ class CWindow {
     Vector2D                 m_vOriginalClosedPos;  // these will be used for calculations later on in
     Vector2D                 m_vOriginalClosedSize; // drawing the closing animations
     SWindowDecorationExtents m_eOriginalClosedExtents;
+    bool                     m_bAnimatingIn = false;
 
     // For pinned (sticky) windows
     bool m_bPinned = false;