[MM-56061] Only render where field in model.AppError when it's present (#25648)

* Only render where field in model.AppError when it's present

* Remove trailing comma from permission error

server/public/model/utils_test.go

@@ -97,6 +97,11 @@ func TestAppErrorRender(t *testing.T) {
 		assert.EqualError(t, aerr, "here: message")
 	})
 
+	t.Run("Without where", func(t *testing.T) {
+		aerr := NewAppError("", "message", nil, "details", http.StatusTeapot)
+		assert.EqualError(t, aerr, "message, details")
+	})
+
 	t.Run("Detailed", func(t *testing.T) {
 		aerr := NewAppError("here", "message", nil, "details", http.StatusTeapot)
 		assert.EqualError(t, aerr, "here: message, details")