[MIRROR] Fixes Build Your Own Shuttle kit [MDB IGNORE] (#16401)

* Fixes Build Your Own Shuttle kit

* Update code/modules/shuttle/shuttle.dm

Co-authored-by: VexingRaven <msgerbs@users.noreply.github.com>
Co-authored-by: Tom <8881105+tf-4@users.noreply.github.com>

code/controllers/subsystem/shuttle.dm

@@ -825,6 +825,8 @@ SUBSYSTEM_DEF(shuttle)
 	preview_shuttle.timer = timer
 	preview_shuttle.mode = mode
 
+	preview_shuttle.postregister(replace)
+
 	// TODO indicate to the user that success happened, rather than just
 	// blanking the modification tab
 	preview_shuttle = null

code/modules/shuttle/emergency.dm

@@ -762,7 +762,7 @@
 		SSshuttle.backup_shuttle = null
 	return ..()
 
-/obj/docking_port/mobile/emergency/shuttle_build/register()
+/obj/docking_port/mobile/emergency/shuttle_build/postregister()
 	. = ..()
 	initiate_docking(SSshuttle.getDock("emergency_home"))
 

code/modules/shuttle/shuttle.dm

@@ -434,6 +434,12 @@
 
 	var/admin_forced = FALSE //SKYRAT EDIT ADDITION
 
+/**
+ * Actions to be taken after shuttle is loaded but before it has been moved out of transit z-level to its final location
+ *
+ * Arguments:
+ * * replace - TRUE if this shuttle is replacing an existing one. FALSE by default.
+ */
 /obj/docking_port/mobile/register(replace = FALSE)
 	. = ..()
 	if(!shuttle_id)
@@ -456,6 +462,15 @@
 
 	SSshuttle.mobile_docking_ports += src
 
+/**
+ * Actions to be taken after shuttle is loaded and has been moved to its final location
+ *
+ * Arguments:
+ * * replace - TRUE if this shuttle is replacing an existing one. FALSE by default.
+ */
+/obj/docking_port/mobile/proc/postregister(replace = FALSE)
+	return
+
 /obj/docking_port/mobile/unregister()
 	. = ..()
 	SSshuttle.mobile_docking_ports -= src