Add whitespace before condition in UserSearchForm

Add whitespace before condition in UserSearchForm

Currently a query like the following is generated:

    SELECT		user_table.userID
    FROM		wcf1_user user_table
    LEFT JOIN	wcf1_user_option_value option_value
    ON		(option_value.userID = user_table.userID)WHERE option_value.userOption4 = ?

This works due to the parentheses around the `ON` part of the `JOIN`, but it
certainly is not pretty and it will cause issues if the parentheses are removed
(as it happened for WoltLab Suite 5.4).

Insert a newline between the base query and the condition to fix the issue.

Resolves #4078

Co-Authored-By: mutec <mysterycode@mysterycode.de>