always use Curl_1st_fatal instead of Curl_1st_err

[icing]

Curl_1st_err() does not return the second error if the first result is CURLE_AGAIN. This may cause errors to not become noticeable when they should be.

Replace all use of Curl_1st_err() with Curl_1st_fatal(), which handles CURLE_AGAIN as a not-a-real-error case.

[Copilot]

Pull request overview

This PR removes Curl_1st_err() and standardizes error-combination logic on Curl_1st_fatal(), fixing cases where a prior CURLE_AGAIN result could mask a subsequent real error (notably in HTTP/3/QUIC egress/expiry paths).

Changes:

• Replaced remaining Curl_1st_err() call sites with Curl_1st_fatal() in QUIC (quiche/ngtcp2) and core transfer paths.
• Removed Curl_1st_err() declaration from lib/url.h and its implementation from lib/url.c.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
lib/vquic/curl_quiche.c	Uses Curl_1st_fatal() when combining CURLE_AGAIN with egress flush results so real errors aren’t masked.
lib/vquic/curl_ngtcp2.c	Uses Curl_1st_fatal() to ensure egress/expiry errors surface even when the main operation yields CURLE_AGAIN.
lib/url.h	Removes the Curl_1st_err() prototype; keeps Curl_1st_fatal() as the supported helper.
lib/url.c	Removes the Curl_1st_err() implementation, leaving Curl_1st_fatal() as the sole helper.
lib/multi.c	Ensures Curl_xfer_write_done() errors aren’t hidden by a prior CURLE_AGAIN.
lib/http.c	Ensures late header-write errors aren’t masked by a prior CURLE_AGAIN.
lib/easy.c	Ensures pause/unpause helper errors aren’t masked by a prior CURLE_AGAIN.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review. Take the survey.