entry: Don't try to handle Tab in entry completions

entry: Don't try to handle Tab in entry completions

Instead, fall through to the default handler after closing the
completion. This has the advantage of letting the file chooser entry
capture the tab key properly, so one can't accidentally move out of the
entry by pressing tab while the completion is popped up.

I also suspect it fixes bugs with weird tab keys and shift/ctrl
oddities. But who knows...