SB 2.0 nightly build #435 with fix of DTL-6609.
There is a remaining problem that when dnd a component into a new column of a GridPane that has ever been emptied, IndexOutOfBoundsException is reported and SB crashes.
snapshot video is attached.

Steps to reproduce:
1. Add a GridPane(2x3).
2. Delete the columns of GridPane one by one, until the last column is deleted.
3. Add a Button to the GridPane on Hierarchy Panel. Now the GridPane is (1x3).
4. Drag a Button to the Content Panel, place it on the right-most side of the GridPane, then there is a vertical gray bar appeared to indicate it's able to add the Button into a new column. (Please refer to the image drop-into-new-column.png.) And release mouse.

SceneBuilder crashes.

Step 4 works fine for the original GridPane.