[MIRROR] [NO GBP] Fixes return values of some chem UI actions. [MDB IGNORE] (#25911)

* [NO GBP] Fixes return values of some chem UI actions. (#80648)

## About The Pull Request
- The chem heater now returns `TRUE` when its buffer dispense volume is
changed thus showing the new value immediately without a 1 second delay
- The debug chem synthesizer also now returns `TRUE` when its amount &
purity values are changed thus showing their new values immediately
without a 1 second delay

## Changelog
🆑
fix: chem heater now shows the new value of its buffer dispense volume
immediately when it gets changed.
fix: debug chem synthesizer now shows the new values of amount & purity
immediately when it gets changed.
/🆑

* [NO GBP] Fixes return values of some chem UI actions.

---------

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

code/modules/reagents/chemistry/machinery/chem_heater.dm

@@ -332,7 +332,7 @@
 				return FALSE
 
 			dispense_volume = target
-			return FALSE
+			return TRUE
 
 /**
  * Injects either acid/base buffer into the beaker

code/modules/reagents/chemistry/machinery/chem_synthesizer.dm

@@ -45,16 +45,28 @@
 			return TRUE
 
 		if("amount")
-			var/input = text2num(params["amount"])
-			if(input)
-				amount = input
-			return FALSE
+			var/input = params["amount"]
+			if(isnull(input))
+				return FALSE
+
+			input = text2num(input)
+			if(isnull(input))
+				return FALSE
+
+			amount = input
+			return TRUE
 
 		if("purity")
-			var/input = text2num(params["amount"])
-			if(input)
-				purity = input
-			return FALSE
+			var/input = params["amount"]
+			if(isnull(input))
+				return FALSE
+
+			input = text2num(input)
+			if(isnull(input))
+				return FALSE
+
+			purity = input
+			return TRUE
 
 	update_appearance()