curl: UAF read in mev_pollset_diff() trace path after curl_easy_pause() in socket callback

Summary: The CVE-2026-9080 fix re-fetches the shentry after the socket callback inside mevshentryupdate, because curleasypause called from that callback re-enters mevassess and can free the entry. The same re-fetch was not applied at the caller, mevpollsetdiff, which dereferences its own entry...