After a click picked the first object with the Blend tool, Escape did
nothing: the pick stayed, and the next click on another object blended
the two. After a blend was made, Escape did not stop the next click
adding to it either.
Escape now drops the object picked first and stops the next click
adding to the blend just made, as a click on empty canvas does, so the
next click picks a new first object. The document and the selection
stay as they are, and no undo step is added.
Docs: docs/mcp.md, docs/target-app-parity.md.