Previously, syncing labels on a message always resulted in updating the
file modification time, even with utime_from_headers=true
This patch restores the file mtime to the previous value when
utime_from_headers=true, preventing a label synchronization from
breaking the promise that the file mtimes coincide with the header date.
Signed-off-by: Abdo Roig-Maranges <abdo.roig@gmail.com>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>