Use regular date when no internal date found
Use regular date when no internal date found

app crashes when trying to fetch "Sent" email folder because the sent
emails don't have an INTERNALDATE field in their summary. In this case
use the envdate field. Fix corresponding parsing function.

Signed-off-by: Aurelien Aptel <b6a68c91a4cbf5ae74d8b878ead861346b35167b@suse.com>

rtucker/imap2maildir,rtucker/imap2maildir