GtkFileChooser: reveal selection after sorting view

After clicking on any of the sort column headers,
the view is properly resorted but the file we had
selected can probably be now out of view due to
the new sort order.

This commit just makes sure to reveal the current
file selection (if any) after the view has been
sorted.

Fixes #2683
7 jobs for BUG_reveal_after_sort_GTK3 in 29 minutes and 53 seconds (queued for 2 seconds)
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