files-view: Disable select-all while loading directory
In the current state, it is possible to perform selection while the directory is loading. In some cases, not all items are selected.
Performing select-all only selects the items that are loaded, till the point of performing the action.
Since the loading state is maintained already, it is easy to do a quick check for any on-going directory loading before performing selection.
Fixes #1389 (closed)