Fix segfault with https and self-signed certs

Crashed when no "/CN=" substring in certificate name.
I saw this with calomel.org (which just had "/C=US", if I recall correctly).

1 files changed, 3 insertions, 2 deletions

diff --git a/dpi/https.c b/dpi/https.c
index e9bf7b5f..d6a16405 100644
--- a/dpi/https.c
+++ b/dpi/https.c
@@ -452,10 +452,11 @@ static int handle_certificate_problem(SSL * ssl_connection)
       case X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT:
          /*Either self signed and untrusted*/
          /*Extract CN from certificate name information*/
-         cn = strstr(remote_cert->name, "/CN=") + 4;
-         if (cn == NULL)
+         if ((cn = strstr(remote_cert->name, "/CN=")) == NULL)
             break;
 
+         cn += 4;
+
          if ((cn_end = strstr(cn, "/")) == NULL )
             cn_end = cn + strlen(cn);