Source credential changes outside of Chocolatey GUI cause issues

If a source is changed to require credentials and the source configuration is not changed prior to opening Chocolatey GUI, it errors on opening as it is attempting to check for updated packages and the source keeps asking for credentials.

Reproduce the issue by changing source credentials outside Chocolatey GUI, then opening the GUI and observing the package-update check. Trace the source configuration and credential handling involved in startup; the issue is done when the GUI opens without repeated credential prompts or errors after an external credential change.

Written by the indexing model from the issue text.