1x1 sprites will not stamp after a "say" block is executed

[adroitwhiz]

Expected Behavior

The "stamp" block should work consistently

Actual Behavior

If a block which causes a speech bubble to appear ("say", "think", "ask") is executed before the "stamp" block, sprites whose texture size is 1x1 will not stamp.

Sprites whose texture size is 1 in one dimension but not the other will produce a 1-pixel line.

This probably has something to do with convex hull calculations.

EDIT: it looks like the "tight" bounds from convex hull calculations are shrunk by one costume-space pixel in all cases.

Steps to Reproduce

https://scratch.mit.edu/projects/348987704/