fix memory corruption in $ssl_client_cert

src/event/ngx_event_openssl.c

diff --git a/src/event/ngx_event_openssl.c b/src/event/ngx_event_openssl.c
index 34d9538..8461140 100644
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -2011,7 +2011,7 @@
 
     p = s->data;
 
-    for (i = 0; i < len; i++) {
+    for (i = 0; i < cert.len - 1; i++) {
         *p++ = cert.data[i];
         if (cert.data[i] == LF) {
             *p++ = '\t';