Before this commit, when hovering on a email icon of a message
in chatter without any customer email data, there was a crash
with the following error message:
"No enumerator given to foreach"
This was caused by `undefined` being passed to `t-foreach` when
there are no customer email data on the message. Since
`undefined == null`, it raised the error above.
closesodoo/odoo#31587
Signed-off-by: =?utf-8?b?QWxleGFuZHJlIEvDvGhuIChha3Up?= <aku@odoo.com>