A gradient mesh with an opacity mask has its own state (`Xy`) after the
mask's dictionary, not right after its `/End X!`. The operators of the
mask's art, on `%_` lines, cleared the flag that says a mesh just ended,
so the state was read as the next object's and each masked mesh in a
run drew with the blend mode of the one before it.
The flag now goes back to what it was when a dictionary opened once it
closes, as `after_object` does.