[PATCH] duphandle: also init netrc

[PATCH] duphandle: also init netrc

The netrc init was only done in the Curl_open, meaning that a duplicated
handle would not get inited properly.

Added test 2309 to verify. It does netrc auth with a duplicated handle.

Regression from 3b43a05e000aa8f65bda513f733a

Reported-by: tranzystorekk on github
Fixes #15496
Closes #15503

Gbp-Pq: Name duphandle_also_init_netrc.patch