only get WAN IP if actually needed

avoid unnecessary traffic

lib.sh

@@ -10,7 +10,9 @@ RUSTDESK_INSTALL_DIR=/var/lib/rustdesk-server
 RUSTDESK_LOG_DIR=/var/log/rustdesk-server
 ARCH=$(uname -m)
 TITLE="RustDesk Linux installer"
+get_wanip4() {
     WANIP4=$(curl -s -k -m 5 -4 https://api64.ipify.org)
+}
 
 ############ Functions