Fix error while validating scrape stage options

lib/frenzy/pipeline/scrape_stage.ex

@@ -39,15 +39,21 @@ defmodule Frenzy.Pipeline.ScrapeStage do
           end
       end
 
-    case opts["convert_to_data_uris"] do
-      nil ->
-        {:ok, %{opts | convert_to_data_uris: true}}
+    case opts do
+      {:ok, opts} ->
+        case opts["convert_to_data_uris"] do
+          nil ->
+            {:ok, %{opts | convert_to_data_uris: true}}
 
-      value when is_boolean(value) ->
-        {:ok, opts}
+          value when is_boolean(value) ->
+            {:ok, opts}
+
+          _ ->
+            {:error, "convert_to_data_uris must be a boolean"}
+        end
 
       _ ->
-        {:error, "convert_to_data_uris must be a boolean"}
+        opts
     end
   end