[Users] Duplicate messages in IMAP Sent folder

[edwardp at gmx.com]

I also ran Claws using --debug. It seems to be saving two copies of the
message, as it's referencing two different message numbers below.

imap.c:1986:Copying messages from Queue to Sent ...
imap.c:527:locking session 0x555daaf708b0 (0)
msgcache.c:271:TIMING msgcache_get_msg_list : 0s000ms
msgcache.c:271:TIMING msgcache_get_msg_list : 0s000ms
imap-thread.c:3299:imap copy - begin
imap-thread.c:457:found imap 0x555daaf09220
imap-thread.c:457:found imap 0x555daaf09220
[2020-09-13 18:46:57] IMAP> 41 UID COPY 284231 Sent
[2020-09-13 18:46:57] IMAP< * 1 EXISTS
[2020-09-13 18:46:57] IMAP< 41 OK [COPYUID 2 284231 291805] UID COPY completed
imap-thread.c:3288:imap copy run - end 0
imap-thread.c:473:generic_cb
imap-thread.c:457:found imap 0x555daaf09220
imap-thread.c:3316:imap copy - end
imap.c:540:unlocking session 0x555daaf708b0
msgcache.c:271:TIMING msgcache_get_msg_list : 0s000ms
msgcache.c:271:TIMING msgcache_get_msg_list : 0s000ms
imap.c:1898:flat imap set: imap.c:1900:284231 imap.c:1902:
imap.c:1898:flat imap set: imap.c:1900:291805 imap.c:1902:
imap.c:2045:copied message 284231 as 291805
file-utils.c:58:TIMING safe_fclose : 0s041ms
imap.c:2066:copied to cache:
/home/user1/.claws-mail/imapcache/imap.mail.yahoo.com/<email_address_redacted>/Sent/291805