Export selection potential fix

[Doublonmousse]

make export selection match the other output modes

There is a minute difference.
On the two other modes we have
if let Some(file)
then we call span_future_local

This was the reverse for the selection export.
Trying to see if this fixes #1199.
I've added a few debug trace to help with debugging for this issue

(it will only be a style PR otherwise)

[Doublonmousse]

This needs to be rewritten to the new glib::clone syntax. Maybe things would work with the new glib version but in the current state, this was rewritten to the new syntax with potentially the same bug.

The fix was confirmed to work.

[flxzt]

isn't the actual fix to change the reference taken by the closure either to a strong reference here and completely remove taking a reference here and move ownership of the selected file into the confirm button callback? I assume saving fails silently because upgrading the reference fails

[flxzt]

I'll follow with a fix and some code cleanup and improved consistency

[Doublonmousse]

The first clone works but not the second one (with the current code).

Honestly, I'm half guessing, for me this was an issue on selected_file being a weak reference and getting dropped (ref count to 0) before the second clone is called.

I think that's similar to what you're proposing, I kinda went with what was done elsewhere (even though I code in rust I can't parse a sentence with two into :))

[flxzt]

my bad that wasn't very clear. take a look at #1227 's code which should do the same thing logically