Adding a handler to detect the unlikely edge case where a message may

have an improperly quoted boundary that can cause the python library to
fail to reproduce the original message with msg.as_bytes().  See:
https://bugs.python.org/issue43818 and
https://github.com/OfflineIMAP/offlineimap3/issues/62

offlineimap/folder/Base.py

@@ -26,6 +26,7 @@ from email import policy
 from email.parser import BytesParser
 from email.generator import BytesGenerator
 from email.utils import parsedate_tz, mktime_tz
+from email.errors import NoBoundaryInMultipartDefect
 
 from offlineimap import threadutil
 from offlineimap.ui import getglobalui