Fixed mail-to regex allowing email addresses to have dots & hyphen as part of the user segment

[lilHermit]

Fixes #5080

[loops]

Hi lilHermit,

This change appears to also allow the hyphen character to precede the @ symbol. However, whenever you want to match an explicit hyphen inside a character-class, the usual practice is to make it the final character of the set. Otherwise, it appears that you're actually trying to match a range of characters, as in [F-T] (all the characters F through T).

Indeed, if you put the proposed regex into the online regex tool at https://rustexp.lpil.uk/ it complains about a boundary error.

It may work as-is, but it's probably worth altering, to move the "-" to the final character after the "." and also mentioning in the commit comment the addition of the hyphen as a valid character before the "@".

[lilHermit]

@loops Good shout, I have now rebased