add install whiptail before update_dialogs

The update_dialogs function depends on whiptail.
whiptail is already in the INSTALLER_DEPS array,
but it gets installed at a later point than here,
so we need to install it for the sake of update_dialogs first.

automated install/basic-install.sh

@@ -892,6 +892,7 @@ if [[ -f ${setupVars} ]];then
   if [ "$1" == "pihole" ]; then
     useUpdateVars=true
   else
+    package_check_install "whiptail"
     update_dialogs
   fi
 fi