Fixes Burrowers being able to use corrosive acid while underground (c…

…mss13-devs#6348)

# About the pull request

Adds an extra check for being burrowed *after* the do_after in corrosive
acid.

Without this (how things are before this PR) it's possible to start
channeling the burrow ability and then start aciding an object, in which
case the acid will finish applying while you're underground since you've
already cleared the check for being burrowed.
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# Explain why it's good for the game

Obviously unintended behavior and I *have* seen people in-game abusing
this.
It's quite awful to play against since there is absolutely zero
counterplay.
# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Put screenshots and videos here with an empty line between the
screenshots and the `<details>` tags.

https://streamable.com/22ualc
</details>


# Changelog
:cl:
fix: Fixed an exploit that allowed Burrowers to apply acid to objects
while underground
/:cl:

code/modules/mob/living/carbon/xenomorph/abilities/ability_helper_procs.dm

@@ -106,6 +106,10 @@
 			to_chat(src, SPAN_WARNING("[A] is already drenched in acid."))
 			return
 
+	if(HAS_TRAIT(src, TRAIT_ABILITY_BURROWED)) //Checked again to account for people trying to place acid while channeling the burrow ability
+		to_chat(src, SPAN_WARNING("We can't melt [O] from here!"))
+		return
+
 	if(!check_state())
 		return