trailing space on username when setting up mtxchat (maybe broader issue with field_placeholder_persist() implementation?

[bunnie]

I was trying to set up a test account and had some trouble because for some reason (not sure why) the username as entered had trailing space. I didn't type it with trailing space -- but in the debug logs I could clearly see there were several trailing spaces on the username.

I suspect there is something wrong with the specific implementation of the modal input method that's adding the trailing space. This needs to be looked into, because it's really confusing for users to debug an issue where they have typed in their username correctly but login is denied because there's trailing space on one of their credential fields.