Object properties don't display when clicking on it if object is already selected

**To reproduce:**
* Select an object to see it's properties
* Select a layer, the layer properties become visible
* Click the object again. The properties do not display.

Reproduce the three selection steps in the Tiled editor and observe the object and layer property panels. Start by tracing the selection and property-display behavior involved in reselecting an object, then verify that the object's properties appear after switching through a layer. Done means the described reproduction no longer leaves the properties hidden.

Written by the indexing model from the issue text.