Scratch-vm: Stamping hidden sprite doesn't do anything

[towerofnix]

Expected Behavior

The sprite's costume should be stamped (with graphic effects).

In the demo project, this should be visible:

Actual Behavior

Nothing is stamped. In the demo project, this is visible:

Note the demo project renders the top row while the sprite is visible, and the bottom row while hidden.

Steps to Reproduce

1. Attempt to stamp a hidden sprite by using the stamp block after the hide block. Alternatively, open and run this project.

Here's the project opened in 2.0, for reference.

Operating System and Browser

macOS 10.12, Google Chrome 56.0.2924.76

[thisandagain]

@liam4 Nice catch!

[joshlory]

No longer repros?

[rschamp]

I wonder what fixed this... good work mystery PR!