wrap: default values for netrc are empty string from python 3.11

From python 3.11 [1]:

> The entry in the netrc file no longer needs to contain all tokens.  The missing
> tokens' value default to an empty string.  All the tokens and their values now
> can contain arbitrary characters, like whitespace and non-ASCII characters.
> If the login name is anonymous, it won't trigger the security check.

[1] 15409c720b

mesonbuild/wrap/wrap.py

@@ -654,7 +654,7 @@ class Resolver:
             return None
 
         login, account, password = self.netrc.authenticators(netloc)
-        if account is not None:
+        if account:
             login = account
 
         return login, password