Invisible toolbox still reports delete area

[alschmiedt]

Describe the bug
When a user sets the toolbox to be not visible the delete area still reports as if the toolbox is there.

To Reproduce

Steps to reproduce the behavior:

1. Go to the playground
2. Drag a block on to the workspace
3. Run Blockly.getMainWorkspace().getToolbox().setVisible(false)
4. Drag the block on the workspace to where the toolbox used to be.
5. Notice how the block is deleted.

Expected behavior
There should not be a delete area where the toolbox used to be.

Screenshots

Stack Traces

Replace with error stack trace.

Additional context
Code sandbox with a temporary fix: https://codesandbox.io/s/relaxed-darkness-rnmy3?file=/src/CustomToolbox.js