Insert space between BASE64 encoded sender name and email address

Fix for https://github.com/opencart/opencart/issues/190. Without a space between the BASE64 encoded sender name and email address spamassassin triggers the FROM_MISSP_REPLYTO and TO_NO_BRKTS_FROM_MSSP rules giving a very high score to the message. This results in messages being caught in junk filters or discarded.