Add missing newline in fallback debug output.

This is hit in case of a recursion in the message handler, and message
hasn't gone through qMessageFormatString at this point and thus lacks
the newline.

Change-Id: Ia098b6ccbcc1aff22a4695865f39143ba0152d9c
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>