Numeric username picked up as commit

@4502040 gets turned into a commit rather than a mention

Directly related to #454 (closed)

Created by: SaintPeter

Getting this as well:

It's not clear to me why a numeric preceeded by an @ should cause the issue. Commits are preceeded by a #

Created by: SaintPeter

Another interesting case: We have a user badc0ded, who's name, of course, is all hexidecimal compatible characters. They render as: null@badc0ded

Also happens with dead23angelwhich transforms into null@dead23a. Thanks to @SerafimArts for the report.