CVE-2026-87861: cross-origin reuse of a Negotiate connection

Summary: I found a cross-origin connection reuse flaw in `lib/url.c`, introduced by [bd10924b4](https://github.com/curl/curl/commit/bd10924b4) as part of the recently announced "Patch the Planet" initiative. It causes a request for one origin to be sent on a connection that was authenticated with …

#ifdef USE_SPNEGO
      if((conn->http_ntlm_state == NTLMSTATE_NONE) &&
         (conn->http_negotiate_state == GSS_AUTHNONE)) {
#else
      if(conn->http_ntlm_state == NTLMSTATE_NONE) {
#endif
        m->found = conn;
      }