Fixes players not being removed from the manifest immediately when cryoing.

* The cryopod simply qdel's the datacore records. Old garbage.dm hard-del()'d datums, so it was fine.  Now we need to make sure they are actually removed from the data_core.
* Testing shows this fixes #1713 and in most cases the objects also GC cleanly.  However some older computers still retain hard references to data_core entries. But even in the cases where that prevents a clean GC, the player is still removed from the manifest successfully and promptly, so that can wait.

code/_helpers/logging.dm

@@ -180,6 +180,8 @@
 	return "[..()] ([ckey])"
 
 /proc/log_info_line(var/datum/d)
+	if(!d)
+		return "*null*"
 	if(!istype(d))
-		return
+		return json_encode(d)
 	return d.log_info_line()