[Bug] Final label on bounding box does not delete with "x"

[jeremydouglass]

The final label -- and only the final label -- on a segment cannot be deleted with its connected "x".

Steps to reproduce:

1. create an Image Segmentation task with an image and bounding box, and two labels: "character" and "dialog"
2. on the image, draw a bounding box.
3. in the pop-up box, label with two labels
4. delete one of the labels using the "x" connected to the label tag (not the dialog "X") -- either label.

It is deleted.

4. try to delete the remaining label, also with the "x" connected to the label tag.

It is NOT deleted.

The final label -- and only the final label -- cannot be deleted with its connected "x".

NOTES:

• This same problem occurs with bounding box, polygon, and expanding line.
• The same problem occurs with any number of tags (2, 4, 8), and it does not matter which tag was added first -- only which tag is left last.
• The workaround is that it can be deleted with the delete-all-labels "X" on the right-hand side of the pop-up box.