Captions sometimes require 2 scans to pick up everything

[cj12312021]

Describe the bug
Sometimes it can take two scans to pick up all provided captions. The problem is that the scene isn't always guaranteed to be processed before its provided captions get processed. If a caption is scanned before the scene it belongs to, that caption doesn't get associated with anything, so a second scan would be required. We could consider waiting to associate the captions found during a scan until the end.

Expected behavior
Captions should be able to get associated correctly with one scan.

Stash Version: v0.15.0:

[WithoutPants]

The current implementation of caption handling also causes an already in transaction error during folder rename detection.

[feederbox826]

Duplicate of #3800 but it seems like a selective scan is needed