SSL: added explicit check for ngx_strlchr() result.

src/event/ngx_event_openssl.c

diff --git a/src/event/ngx_event_openssl.c b/src/event/ngx_event_openssl.c
index 1d2d1ef..f885a5c 100644
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -2637,6 +2637,11 @@
 
         end = s + slen;
         s = ngx_strlchr(s, end, '.');
+
+        if (s == NULL) {
+            return NGX_ERROR;
+        }
+
         slen = end - s;
 
         if (plen == slen && ngx_strncasecmp(s, p, plen) == 0) {