Fix crash that can occur with schemas that only have a single field

lib/kaffy/resource_schema.ex

@@ -88,18 +88,21 @@ defmodule Kaffy.ResourceSchema do
   end
 
   defp reorder_fields(fields_list, schema) do
-    [_id, first_field | _fields] = schema.__schema__(:fields)
-
-    # this is a "nice" feature to re-order the default fields to put the specified fields at the top/bottom of the form
-    fields_list
-    |> reorder_field(first_field, :first)
-    |> reorder_field(:email, :first)
-    |> reorder_field(:name, :first)
-    |> reorder_field(:title, :first)
-    |> reorder_field(:id, :first)
-    |> reorder_field(:inserted_at, :last)
-    |> reorder_field(:updated_at, :last)
+    if length(schema.__schema__(:fields)) > 1 do
+      [_id, first_field | _fields] = schema.__schema__(:fields)
 
+      # this is a "nice" feature to re-order the default fields to put the specified fields at the top/bottom of the form
+      fields_list
+      |> reorder_field(first_field, :first)
+      |> reorder_field(:email, :first)
+      |> reorder_field(:name, :first)
+      |> reorder_field(:title, :first)
+      |> reorder_field(:id, :first)
+      |> reorder_field(:inserted_at, :last)
+      |> reorder_field(:updated_at, :last)
+    else
+      fields_list
+    end
     # |> reorder_field(Kaffy.ResourceSchema.embeds(schema), :last)
   end