est_change will fail if at least one of the parameters has been labelled

[sfcheung]

To-Do

• [x] Write a test in which some parameters were labelled. (c71e739e918fbc0741f553c0189cd9f8498acb22)
• [x] Revise est_change. (c71e739e918fbc0741f553c0189cd9f8498acb22)

It is because vcov(lavaan-class object) will use the labels if it is present. Need to revise est_change to consider the presence of labels.

Note

• est_change_raw is not affected because it does not call vcov.