Fixed REPLACE logic to now match MySQL

[Hydrocharged]

Previously we thought that REPLACE was a DELETE then INSERT, but this is not the actual order that MySQL takes. According to the MySQL documentation (https://dev.mysql.com/doc/refman/8.0/en/replace.html):

 MySQL uses the following algorithm for REPLACE (and LOAD DATA ... REPLACE):

    Try to insert the new row into the table

    While the insertion fails because a duplicate-key error occurs for a primary key or unique index:

        Delete from the table the conflicting row that has the duplicate key value

        Try again to insert the new row into the table 

Special emphasis on the While, as you have to keep trying until you either get a different error, or it succeeds. So this has now been duplicated.