[FIX] fetchmail: prevent onchange for erasing server name

currently, in fetchmail while create an incoming
mail server, Set a server name while being in POP
or IMAP server type and Switch to "Local" server type
the server name is erased.

with this commit, the value of the server name
should not be erased with onchange.

closes odoo/odoo#69250

Taskid: 2258523
X-original-commit: cf102783b43a44a38565768129ef414758a71fc6
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/fetchmail/models/fetchmail.py

@@ -64,8 +64,6 @@ class FetchmailServer(models.Model):
             self.port = self.is_ssl and 995 or 110
         elif self.server_type == 'imap':
             self.port = self.is_ssl and 993 or 143
-        else:
-            self.server = ''
 
         conf = {
             'dbname': self.env.cr.dbname,