[FIX] mail: reload messages after closing composer

Always reload the message after the mail composer message is closed.

Since there is several unrelated model it would probably messy to go
from the mail thread to the mail composer popup to see if a new message
is posted (or get it and add it in the chatter like done in the simple
message editor).

With this change, anytime the mail composer modal is closed the mail
thread messages are reloaded.

closes #7596
opw-644406