setopt: clear the "custom" CA booleans when set to NULL

[bagder]

Mark them as custom choices only when pointer is passed, and clear them again when set to NULL.

[Copilot]

Pull request overview

This PR adjusts how libcurl tracks whether CA bundle/path/blob settings are “custom” by setting the custom_* booleans based on whether a non-NULL pointer/blob is provided, and clearing those flags again when the option is set to NULL. This matters because these flags influence later default CA / native store configuration decisions in the TLS setup logic.

Changes:

• Update CURLOPT_CAINFO / CURLOPT_PROXY_CAINFO to set custom_cafile based on whether ptr is non-NULL.
• Update CURLOPT_CAPATH / CURLOPT_PROXY_CAPATH to set custom_capath based on whether ptr is non-NULL.
• Update CURLOPT_CAINFO_BLOB / CURLOPT_PROXY_CAINFO_BLOB to set custom_cablob based on whether blob is non-NULL.

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[icing]

I think this does not address the problem. Let me have a stab at it.

Update: proposing #21902

[bagder]

@icing right, but still it seems to be correct to reset these booleans when we set these options back to NULL, right?

[icing]

@icing right, but still it seems to be correct to reset these booleans when we set these options back to NULL, right?

Yes, indeed.