openssl: fix infof() to avoid compiler warning for %s with null
vtls/openssl.c: In function ‘ossl_connect_step2’:
../lib/curl_trc.h:120:10: error: ‘%s’ directive argument is null [-Werror=format-overflow=]
120 | Curl_infof(data, __VA_ARGS__); } while(0)
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
vtls/openssl.c:4008:5: note: in expansion of macro ‘infof’
4008 | infof(data, "SSL connection using %s / %s / %s / %s",
| ^~~~~
vtls/openssl.c:4008:49: note: format string is defined here
4008 | infof(data, "SSL connection using %s / %s / %s / %s",
| ^~
Follow-up to b6e6d4ff8f
Closes #12196