Handle the case where `--netrc-file` isn't a file on disk

[P-E-Meunier]

I did this

curl -L --netrc-file <(cat /tmp/netrc) https://some-url.com, where https://some-url.com redirects me to https://other-host.com.

I expected the following

I expected the credentials from my netrc file to be used on https://other-host.com, but they were not.

My understanding is that libcurl expects netrc files to be actual files that can be read multiple times, which may not be the case. An actual use case for this is a GPG-encrypted netrc file, in the same format Git uses.

curl/libcurl version

commit 436bbbe (latest on master today)

operating system

Linux pem 6.6.52 #1-NixOS SMP Wed Sep 18 17:24:10 UTC 2024 aarch64 GNU/Linux