Tracker: Check whether the default button is disabled on double-click.

The comment above this block specified the correct behavior: the
button's status is already updated elsewhere, so just check IsEnabled().
But the code did not actually do that.

It appears this has been incorrect all the way back to the initial
OpenTracker import in 2001.

Fixes #13721.

src/kits/tracker/FilePanelPriv.cpp

@@ -1261,7 +1261,7 @@ TFilePanel::MessageReceived(BMessage* message)
 						// all we have to do is see if the button is enabled.
 						BButton* button = dynamic_cast<BButton*>(
 							FindView("default button"));
-						if (button == NULL)
+						if (button == NULL || !button->IsEnabled())
 							break;
 
 						if (IsSavePanel()) {