Fixes #2369 (#2372)

I suspect the issue is with null entries in the records list.

This just nukes them all before processing with sorting. I looked over all of the list accesses, and they didn't appear to be index controlled, so this shouldn't break anything.

code/datums/mixed.dm

@@ -21,8 +21,19 @@
 /datum/data/record
 	name = "record"
 	size = 5.0
-	var/list/fields = list(  )
+	var/list/fields = list()
+	var/inDataCore = 0
 
+/datum/data/record/Destroy()
+	// Just remove us from everywhere. So we don't have to keep track of which list
+	// we're in specifically.
+	if (inDataCore && data_core)
+		data_core.general	-= src
+		data_core.medical	-= src
+		data_core.security	-= src
+		data_core.locked	-= src
+
+	return ..()
 
 /datum/data/text
 	name = "text"