[effects] Ensure the correct cursor shape is set for mouse interception

When starting mouse interception the window might already be created
in which case the cursor wasn't defined. So let's always set it.

REVIEW: 12232

effects.cpp

@@ -690,6 +690,8 @@ void EffectsHandlerImpl::startMouseInterception(Effect *effect, Qt::CursorShape
             Cursor::x11Cursor(shape)
         };
         m_mouseInterceptionWindow.reset(Xcb::createInputWindow(geo, mask, values));
+    } else {
+        defineCursor(shape);
     }
     m_mouseInterceptionWindow.map();
     m_mouseInterceptionWindow.raise();