Improve error messages when adding a non-valid source URL (#436)

lib/pinchflat/sources/sources.ex

@@ -186,7 +186,13 @@ defmodule Pinchflat.Sources do
       {:ok, source_details} ->
         add_source_details_by_collection_type(source, changeset, source_details)
 
-      {:error, runner_error, _status_code} ->
+      err ->
+        runner_error =
+          case err do
+            {:error, error_msg, _status_code} -> error_msg
+            {:error, error_msg} -> error_msg
+          end
+
         Ecto.Changeset.add_error(
           changeset,
           :original_url,