gluon-web-model: fix Warning field not being hidden

"not self.title" doesn't work because of "self.title = title or """

package/gluon-web-model/files/lib/gluon/web/view/model/warning.html

@@ -1,4 +1,4 @@
-<%- if self.title or self.content then -%>
+<%- if not self.hide then -%>
 <div class="gluon-warning"<%=
 	attr("id", id) ..
 	attr("data-index", self.index) ..

package/gluon-web-private-wifi/luasrc/lib/gluon/config-mode/model/admin/privatewifi.lua

@@ -27,10 +27,11 @@ local enabled = s:option(Flag, "enabled", translate("Enabled"))
 enabled.default = uci:get('wireless', primary_iface) and not uci:get_bool('wireless', primary_iface, "disabled")
 
 local warning = s:element('model/warning', {
-	content = mesh_on_wan and translate(
+	content = translate(
 		'Meshing on WAN interface is enabled. ' ..
 		'This can lead to problems.'
-	) or nil,
+	),
+	hide = not mesh_on_wan,
 }, 'warning')
 warning:depends(enabled, true)