gui: Don't increment change index when running (auto) coin selection

[jp1ac4]

This relates to #563 (comment).

Currently, when a user is creating a new spend, the GUI may call create_spend several times in order to select coins automatically each time the user edits the input values. Each time create_spend is called, the next change index in the DB is incremented.

Following #821, we can now fix the change address to use when calling create_spend. We could use this to prevent the change index incrementing on these intermediate calls to create_spend. We could either pass an arbitrary change address, e.g. for index 0, or we could get the next change address from the DB and use this.

[darosior]

I think this was fixed by #863. @jp1ac4 can you confirm and close this issue if so?

[jp1ac4]

Yep, this has been fixed.

For future reference, it should be noted that once a draft PSBT has been generated (so after clicking Next on the Send page), the change index will be incremented if this draft PSBT has a change output (see also #963).