merge: upstream fixes (mutt/default)

 * clang-format
 * Display an error message when delete mailbox fails. (see #3968)
 * Updated French translation.
 * Fix imap sync segfault due to inactive headers during an expunge. (closes #3971)
 * Close the imap socket for the selected mailbox on error.
 * Add missing IMAP_CMD_POLL flag in imap buffy check.
 * Change maildir and mh check_mailbox to use dynamic sized hash. (closes #3973)