Fixed a 'BAD Invalid field-name' bug that in some cases could occur

Fixed an imap bug that in some cases could occur ('BAD Invalid field-name in UID Fetch BODY.PEEK[HEADER.FIELDS' due to field-names being separated by 2 spaces) because of which no messages will be listed.

[16-Apr-2014 16:23:00 +0100]: [0095] C: A0008 UID FETCH 1:25 (UID RFC822.SIZE FLAGS INTERNALDATE BODY.PEEK[HEADER.FIELDS (DATE FROM TO SUBJECT CONTENT-TYPE CC REPLY-TO LIST-POST DISPOSITION-NOTIFICATION-TO X-PRIORITY  X-ORIGINAL-TO)])
[16-Apr-2014 16:23:00 +0100]: [0095] S: A0008 BAD Invalid field-name in UID Fetch BODY.PEEK[HEADER.FIELDS