In 72cd8d076 there was an improvement for removing infinite loop in POP
mail server, but if there was no message to fetch, you can get an error:
UnboundLocalError: local variable 'num' referenced before assignment
because `num` is not set when logging stats of fetching mails.
`num` should be set to 0 by default, we don't want to have it unset or
use a value from a previous loop.
opw-2724216
closesodoo/odoo#82582
X-original-commit: 7b3b623cf3359ac1eea537177f7f963e81403a01
Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>