fix: more robust <app> autocomplete + error handling

See toolshed/organising#652

cli/app/rollback.go

@@ -46,8 +46,8 @@ beforehand.`,
 		case 1:
 			app, err := appPkg.Get(args[0])
 			if err != nil {
-				log.Debugf("autocomplete failed: %s", err)
-				return nil, cobra.ShellCompDirectiveDefault
+				errMsg := fmt.Sprintf("autocomplete failed: %s", err)
+				return []string{errMsg}, cobra.ShellCompDirectiveError
 			}
 			return autocomplete.RecipeVersionComplete(app.Recipe.Name)
 		default: