CreateEnvironmentBlock failure should be handled and reported

[fasterthanlime]

There's this weird thing on Windows where it won't let you programatically log in as another user more than once (at least, it won't let you CreateEnvironmentBlock if there's already a process running as that user, spawned with CreateProcessWithLogonW).

Maybe there's a solution to that (like, have elevate be a daemon?), but if not, that error condition should be detected since it's (relatively) well-understood now

[fasterthanlime]

Note: a workaround can be provided by doing:

taskkill /F /FI "USERNAME eq itch-player-57e29d63"

(with the right itch-player-, obviously)

[fasterthanlime]

This is especially useful because there can be some processes still running as itch-player-* that aren't even visible in process explorer, and rebooting is a shitty workaround.

[fasterthanlime]

butler handles this in v25, and properly propagates errors.