Scene Editor block tool doesn't allow dragging out blocks on terrain

[chrisspieler]

Describe the bug

If you use the block tool in the scene editor on empty space, a block is created. If you use the block tool on terrain, no block is created.

To Reproduce

1. Open the attached project (just an empty scene with some terrain)
2. Open main.scene
3. Use the block tool to drag out a block on the terrain
4. See that the terrain doesn't allow you to start dragging shapes

Expected behavior

It should be possible to draw a block in a spot where terrain exists.

Media/Files

my_cool_repro.zip

Additional context

For my current use case, I just want the block that's created over terrain to be axis-aligned, so it's fine with me if this bug is fixed by just ignoring the terrain altogether.

[chrisspieler]

This is a duplicate of: #5106