[MIRROR] Fixes envelope & reagent holder interaction (#26976)

* Fixes envelope & reagent holder interaction (#82127)

## About The Pull Request
- Fixes #82122

This is a 2 part fix.
- Reagent holders (cup & syringe the only cases i can find) will update
the target appearance only when their action succeeds. This way they
don't cause items like envelops to update after every interaction.
- Envelope returns the stamp overlay in the return value of
`update_overlays()` rather than calling `add_overlay()` so their
overlays don't add up but rather get removed & replaced correctly.

## Changelog
🆑
fix: reagent containers like cup & syringe only update target appearance
if action was successful.
fix: envelops don't stack overlays when interacting with cup & syringes.
/🆑

* Fixes envelope & reagent holder interaction

---------

Co-authored-by: SyncIt21 <110812394+SyncIt21@users.noreply.github.com>

code/game/objects/items/mail.dm

@@ -87,8 +87,8 @@
 			pixel_y = stamp_offset_y + bonus_stamp_offset
 		)
 		stamp_image.appearance_flags |= RESET_COLOR
-		add_overlay(stamp_image)
 		bonus_stamp_offset -= 5
+		. += stamp_image
 
 	if(postmarked == TRUE)
 		var/image/postmark_image = image(
@@ -98,7 +98,7 @@
 			pixel_y = stamp_offset_y + rand(bonus_stamp_offset + 3, 1)
 		)
 		postmark_image.appearance_flags |= RESET_COLOR
-		add_overlay(postmark_image)
+		. += postmark_image
 
 /obj/item/mail/attackby(obj/item/W, mob/user, params)
 	// Destination tagging

code/modules/reagents/reagent_containers/cups/_cup.dm

@@ -127,6 +127,7 @@
 		var/trans = reagents.trans_to(target, amount_per_transfer_from_this, transferred_by = user)
 		to_chat(user, span_notice("You transfer [trans] unit\s of the solution to [target]."))
 		SEND_SIGNAL(src, COMSIG_REAGENTS_CUP_TRANSFER_TO, target)
+		target.update_appearance()
 
 	else if(target.is_drainable()) //A dispenser. Transfer FROM it TO us.
 		if(!target.reagents.total_volume)
@@ -140,8 +141,7 @@
 		var/trans = target.reagents.trans_to(src, amount_per_transfer_from_this, transferred_by = user)
 		to_chat(user, span_notice("You fill [src] with [trans] unit\s of the contents of [target]."))
 		SEND_SIGNAL(src, COMSIG_REAGENTS_CUP_TRANSFER_FROM, target)
-
-	target.update_appearance()
+		target.update_appearance()
 
 /obj/item/reagent_containers/cup/afterattack_secondary(atom/target, mob/user, proximity_flag, click_parameters)
 	if((!proximity_flag) || !check_allowed_items(target, target_self = TRUE))

code/modules/reagents/reagent_containers/syringes.dm

@@ -82,9 +82,10 @@
 			living_target.log_message("injected themselves ([contained]) with [name]", LOG_ATTACK, color="orange")
 		else
 			log_combat(user, living_target, "injected", src, addition="which had [contained]")
-	reagents.trans_to(target, amount_per_transfer_from_this, transferred_by = user, methods = INJECT)
-	to_chat(user, span_notice("You inject [amount_per_transfer_from_this] units of the solution. The syringe now contains [reagents.total_volume] units."))
-	target.update_appearance()
+
+	if(reagents.trans_to(target, amount_per_transfer_from_this, transferred_by = user, methods = INJECT))
+		to_chat(user, span_notice("You inject [amount_per_transfer_from_this] units of the solution. The syringe now contains [reagents.total_volume] units."))
+		target.update_appearance()
 
 /obj/item/reagent_containers/syringe/afterattack_secondary(atom/target, mob/user, proximity_flag, click_parameters)
 	if (!try_syringe(target, user, proximity_flag))