Fix a warning about an uninit var

Reviewed-by: NRichard Levitte <levitte@openssl.org>

test/clienthellotest.c

@@ -32,7 +32,7 @@
 int main(int argc, char *argv[])
 {
     SSL_CTX *ctx;
-    SSL *con;
+    SSL *con = NULL;
     BIO *rbio;
     BIO *wbio;
     BIO *err;