gluon-config-mode: fix wizard

Due to my previous two commits configmode was broken when either meshvpn
or bandwidth limit was disabled. This fixes it but there may be a
cleaner solution provided by luci.

package/gluon-config-mode/files/usr/lib/lua/luci/model/cbi/gluon-config-mode/wizard.lua

@@ -69,12 +69,22 @@ function f.handle(self, state, data)
     uci:save("autoupdater")
     uci:commit("autoupdater")
 
+    -- checks for nil needed due to o:depends(...)
+    if data._limit_enabled ~= nil then
       uci:set("gluon-simple-tc", meshvpn_name, "interface")
       uci:set("gluon-simple-tc", meshvpn_name, "enabled", data._limit_enabled)
       uci:set("gluon-simple-tc", meshvpn_name, "ifname", "mesh-vpn")
+
+      if data._limit_ingress ~= nil then
         uci:set("gluon-simple-tc", meshvpn_name, "limit_ingress", data._limit_ingress)
+      end
+
+      if data._limit_egress ~= nil then
         uci:set("gluon-simple-tc", meshvpn_name, "limit_egress", data._limit_egress)
+      end
+
       uci:commit("gluon-simple-tc")
+    end
 
     uci:set("fastd", meshvpn_name, "enabled", data._meshvpn)
     uci:save("fastd")