api: improve error handling when compose push fails

There was missing condition for the case when compose push fails.
As the previous commit introduces customizations which can return even more
errors it is important to report such errors.

For now the API is returning only 500 HTTP code. In future we should
distinguish between failures and blueprint validation errors.

internal/store/store.go

@@ -382,7 +382,7 @@ func (s *Store) PushCompose(composeID uuid.UUID, bp *blueprint.Blueprint, compos
 	}
 	pipeline, err := bp.ToPipeline(composeType)
 	if err != nil {
-		return &InvalidRequestError{"invalid output type: " + composeType}
+		return err
 	}
 	s.change(func() error {
 		s.Composes[composeID] = Compose{

internal/weldr/api.go

@@ -757,7 +757,19 @@ func (api *API) composeHandler(writer http.ResponseWriter, httpRequest *http.Req
 	found := api.store.GetBlueprint(cr.BlueprintName, &bp, &changed) // TODO: what to do with changed?
 
 	if found {
-		api.store.PushCompose(reply.BuildID, &bp, cr.ComposeType)
+		err := api.store.PushCompose(reply.BuildID, &bp, cr.ComposeType)
+
+		// TODO: we should probably do some kind of blueprint validation in future
+		// for now, let's just 500 and bail out
+		if err != nil {
+			log.Println("error when pushing new compose: ", err.Error())
+			errors := responseError{
+				ID:  "ComposePushErrored",
+				Msg: err.Error(),
+			}
+			statusResponseError(writer, http.StatusInternalServerError, errors)
+			return
+		}
 	} else {
 		errors := responseError{
 			ID:  "UnknownBlueprint",