Fixes being gibbed sometimes breaking observer movement

[SabreML]

About the pull request

Fixes a bug where having holding down the Ctrl or Alt key, being gibbed, then releasing the key could completely prevent you from moving. (Until you relog or respawn)

This was caused by /datum/keybinding/mob/prevent_movement's down()/up() procs returning early if the user's body was an observer.
In this case, user.movement_locked gets set to TRUE while the user has a body, the body gets gibbed and the user is forced into an observer, and then the proc is unable to set it back to FALSE.

cmss13/code/datums/keybinding/mob.dm

Lines 229 to 239 in 93a1a8b

	/datum/keybinding/mob/prevent_movement/down(client/user)
	. = ..()
	if(.)
	return
	user.movement_locked = TRUE
	/datum/keybinding/mob/prevent_movement/up(client/user)
	. = ..()
	if(.)
	return
	user.movement_locked = FALSE

---

Having spent a while looking around the codebase, I'm almost certain that removing the isobserver() checks won't have any negative side effects. Despite that, this PR should maybe get testmerged anyway just in case it does.

Explain why it's good for the game

Observers should be able to move around.

Testing Photographs and Procedure

Screenshots & Videos

NOTE: These videos aren't the best at showing what's happening since you can't see my keyboard inputs, so for reference I started holding Ctrl before pressing 'Yes', then released it after the facehugger gibbed.

Before:

dreamseeker_cGbBIblGjW.mp4

After:

dreamseeker_V7Xmyx4Nbl.mp4

Changelog

🆑
fix: Fixed being gibbed with the Ctrl or Alt key held sometimes breaking movement as an observer.
/:cl: