mssql named instance port number

[adi1]

Describe the bug
When connecting to an mssql named instance, the connection string generated in tortoise.mssql.client.MSSQLClient still includes the port number. Named instances listen on dynamic ports, so the ,{port} should be left out, otherwise it tries to connect by default to port 1433 which fails.

To Reproduce
Create an mssql connection with host containing a named instance, for example my_server\my_instance

Expected behavior
It should work

Additional context
One possible fix could be:

    if "\\" in host:
        # named instance, don't provide port
        server = host
    else:
        server = f"{host},{port}"
    self.dsn = f"DRIVER={driver};SERVER={server};UID={user};PWD={password};"