"Fixes" Subshuttle Error (#2477)

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guard clause :)
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code/modules/overmap/ships/controlled_ship_datum.dm

@@ -77,6 +77,8 @@
 		shuttle_area.rename_area("[new_name] [initial(shuttle_area.name)]")
 	if(!force)
 		COOLDOWN_START(src, rename_cooldown, 5 MINUTES)
+		if(shuttle_port.virtual_z() == null)
+			return TRUE
 		priority_announce("The [oldname] has been renamed to the [new_name].", "Docking Announcement", sender_override = new_name, zlevel = shuttle_port.virtual_z())
 	return TRUE