Unsaved scripts were previously displayed with blank tabs, which are
mostly a result of deleted or improperly moved scripts.
This patch makes sure that those kind of scripts are displayed as
"[unsaved]" now, and ensures that scripts are removed from the list
while deleting scripts from the filesystem dock preventing the unsaved
tabs to appear in the first place (a user is already prompted with
"no undo" warning while deleting any file).
A user is always prompted to save those "[unsaved]" scripts if they
attempt to close them without saving in any case except as described
above.
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