correction for openssl_x509_parse vs. UTC

Summary:
While testing HHVM on a different machine I noticed a regression failure in
hphp/test/zend/good/ext/openssl/tests/openssl_x509_parse_basic.php

side-by-side testing with gdb on the two systems working/not working shows that
down in the extension the certificate is parsed the same way until the final daylight
savings time adjustment.  The difference between the two systems was the timezone
setting.  There should be no adjustment when the system setting is UTC.

BEFORE
======
root@xyzzy:/mnt/cdn/hhvm/hhvm# timedatectl set-timezone UTC
root@xyzzy:/mnt/cdn/hhvm/hhvm# timedatectl
      Local time: Fri 2017-04-14 16:02:42 UTC
  Universal time: Fri 2017-04-14 16:02:42 UTC
        RTC time: Fri 2017-04-14 15:15:04
       Time zone: UTC (UTC, +0000)
 Network time on: yes
NTP synchronized: yes
 RTC in local TZ: no

root@xyzzy:/mnt/cdn/hhvm/hhvm# /mnt/cdn/hhvm/hhvm/hphp/hhvm/hhvm /mnt/cdn/hhvm/hhvm/hphp/test/run  /mnt/cdn/hhvm/hhvm/hphp/test/zend/good/ex
Closes #7785

Differential Revision: D4891689

Pulled By: Orvid

fbshipit-source-id: 7d0c6448134676e594a59c003673c37d77a9d560

hphp/runtime/ext/openssl/ext_openssl.cpp

@@ -2553,7 +2553,8 @@ static time_t asn1_time_to_time_t(ASN1_UTCTIME *timestr) {
   gmadjust = -(thetime.tm_isdst ?
                (long)timezone - 3600 : (long)timezone);
 #endif
-  ret += gmadjust;
+  /* no adjustment for UTC */
+  if (timezone) ret += gmadjust;
   free(strbuf);
   return ret;
 }