[NetworkManager-openconnect] Fix crash on protocol being unset

[David Woodhouse <dwmw2 src gnome org>]

commit d3c982aba6180c5a7afd575d7c3e0c9cb3265008
Author: David Woodhouse <dwmw2 infradead org>
Date:   Tue Oct 16 09:55:06 2018 -0700

    Fix crash on protocol being unset

 auth-dialog/main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/auth-dialog/main.c b/auth-dialog/main.c
index d87f39b..c69f729 100644
--- a/auth-dialog/main.c
+++ b/auth-dialog/main.c
@@ -1079,7 +1079,7 @@ static int get_config (auth_ui_data *ui_data,
 
        protocol = g_hash_table_lookup (options, NM_OPENCONNECT_KEY_PROTOCOL);
 #if OPENCONNECT_CHECK_VER(5,1)
-       if (openconnect_set_protocol(vpninfo, protocol))
+       if (protocol && openconnect_set_protocol(vpninfo, protocol))
 #else
        if (protocol && strcmp(protocol, "anyconnect"))
 #endif