Fixed Select None action to be enabled when there is any selection

The "Select None" action clears both the tile and the object selection,
but it was only enabled based on either selection, depending on the type
of the current layer. Now it always checks both types of selection.

src/tiled/mapdocumentactionhandler.cpp

@@ -721,19 +721,7 @@ void MapDocumentActionHandler::updateActions()
 
     mActionSelectAll->setEnabled(map);
     mActionSelectInverse->setEnabled(map);
-
-    if (currentLayer) {
-        if (currentLayer->asTileLayer()) {
-            mActionSelectNone->setEnabled(!selection.isEmpty());
-        } else if (currentLayer->asObjectGroup()) {
-            mActionSelectNone->setEnabled(selectedObjectsCount  > 0);
-        } else {
-            mActionSelectNone->setEnabled(false);
-        }
-    } else {
-        mActionSelectNone->setEnabled(false);
-    }
-
+    mActionSelectNone->setEnabled(!selection.isEmpty() || selectedObjectsCount  > 0);
 
     mActionCropToSelection->setEnabled(!selection.isEmpty());