test1540: valgrind reporting errors in CI

[vszakats]

I did this

Noticed test1540 failures not seen earlier:
https://github.com/curl/curl/actions/runs/16555854300?pr=18042
https://github.com/curl/curl/actions/runs/16556629015/job/46818974026?pr=18047
https://github.com/curl/curl/actions/runs/16556860012/job/46819517495?pr=17927

Example runs on master:
https://github.com/curl/curl/actions/runs/16553316775
https://github.com/curl/curl/actions/runs/16553423741
https://github.com/curl/curl/actions/runs/16555354310
history:
https://github.com/curl/curl/actions/workflows/linux.yml?query=branch%3Amaster

With TLS backends: wolfssl-opensslextra, mbedtls, openssl, libressl

[...]
 16:53:25.146457 == Info: WARNING: no socket in pollset or timer, transfer may stall
 libtests: ../../lib/multi.c:1120: Curl_multi_getsock: Assertion `0' failed.
 Aborted (core dumped)
=== End of file stderr1540
=== Start of file valgrind1540
 ==100982== 17 bytes in 1 blocks are possibly lost in loss record 5 of 122
 ==100982==    at 0x4846828: malloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
 ==100982==    by 0x48E2937: curl_dbg_malloc (memdebug.c:147)
 ==100982==    by 0x48E2B81: curl_dbg_strdup (memdebug.c:202)
 ==100982==    by 0x492C1FA: set_login (url.c:2933)
 ==100982==    by 0x492DAE4: create_conn (url.c:3579)
 ==100982==    by 0x492E748: Curl_connect (url.c:3910)
 ==100982==    by 0x48F1392: state_connect (multi.c:2252)
 ==100982==    by 0x48F185E: multi_runsingle (multi.c:2380)
 ==100982==    by 0x48F25E2: curl_multi_perform (multi.c:2735)
 ==100982==    by 0x48A58BE: easy_transfer (easy.c:705)
 ==100982==    by 0x48A5C13: easy_perform (easy.c:813)
 ==100982==    by 0x48A5C7E: curl_easy_perform (easy.c:832)
 ==100982==    by 0x14AAA8: test_lib1540 (lib1540.c:115)
 ==100982==    by 0x17F5CC: main (first.c:167)
[...and more...]

FAIL 1540: 'chunked with trailers and pausing the receive' HTTP, HTTP GET, CURLPAUSE_RECV, chunked Transfer-Encoding, Trailer:, DELAY

I expected the following

test1540 to pass.

curl/libcurl version

master, first seen at commit 6080143

it was preceded by another multi-related commit: 0122cc1

(their PRs didn't trigger valgrind AFAICS)

operating system

seen on Linux

[bagder]

This does not reproduce for me...

[vszakats]

This does not reproduce for me...

In CI it's flaky. Seen disappearing after a relaunch:
https://github.com/curl/curl/actions/runs/16556860012/job/46836595732?pr=17927