tiling: Add fallback path for the first Polonium tile

After !5532 a new code path was triggered during Workspace::rearrange call.
When first Polonium window opens on any screen, there is no active tile yet.
This forces geometry calculation in Window::checkWorkspacePosition -> Window::ensureSpecialStateGeometry
To return empty QRect, which depending on the screen arrangement will move window to the other screen.

This confuses Polonium plugin, as it receives wrong outputChanged signal in scripting API.

BUG: 488898
Signed-off-by: Alik Aslanyan <inline0@pm.me>

src/window.cpp

@@ -3398,8 +3398,6 @@ QRectF Window::quickTileGeometry(QuickTileMode mode, const QPointF &pos) const
         Tile *tile = workspace()->tileManager(output)->bestTileForPosition(pos);
         if (tile) {
             return tile->windowGeometry();
-        } else {
-            return QRectF();
         }
     }