Resolve "Search function on patient page broken"

What does this MR do?

Searching patients was broken due to the equality check for mail regardless of whether this was included or not.

Actions taken to fix the bug

Only check for the mail if the user has provided an email.

Does this MR meet the acceptance criteria?

• I have added tests to validate the fix.
• I have updated the documentation accordingly.
• I have added translations for all new client-side text. Closes #150 (closed)