Better client side validation when '<', '>' found in the email field (user search dialog)

Right now the user receives a reportable error when they (probably) copy-paste the email address of the user into the email field of the search user dialog: `John Doe `

No file or test is named. Reproduce the issue in the user search dialog by pasting `John Doe ` into the email field, then trace the existing client-side validation. Done means this input is handled by validation instead of producing a reportable error.

Written by the indexing model from the issue text.