Another bunch of fixes for TGUI inputs (I'll be cursed...) (#25009)

* Oh god, oh fuck, WHY DIDN'T I USE isnull()???

* More correct checks

* That's all

* That's all x2

* Flavor fix

code/modules/pda/cart_apps.dm

@@ -26,11 +26,11 @@
 				switch(text2num(params["msgnum"]))
 					if(1)
 						message1 = tgui_input_text(usr, "Line 1", "Enter Message Text", message1, encode = FALSE)
-						if(!message1)
+						if(isnull(message1))
 							return
 					if(2)
 						message2 = tgui_input_text(usr, "Line 2", "Enter Message Text", message2, encode = FALSE)
-						if(!message2)
+						if(isnull(message2))
 							return
 
 		if("Status")

code/modules/pda/core_apps.dm

@@ -74,7 +74,7 @@
 	switch(action)
 		if("Edit")
 			var/n = tgui_input_text(usr, "Please enter message", name, note, multiline = TRUE, encode = FALSE)
-			if(!n)
+			if(isnull(n))
 				return
 
 			if(pda.loc == usr)

code/modules/pda/messenger.dm

@@ -122,8 +122,6 @@
 
 /datum/data/pda/app/messenger/proc/create_message(mob/living/U, obj/item/pda/P)
 	var/t = tgui_input_text(U, "Please enter your message", name)
-	if(!t)
-		return
 	if(!t || !istype(P))
 		return
 	if(!in_range(pda, U) && pda.loc != U)

code/modules/pda/nanobank.dm

@@ -242,7 +242,7 @@
 
 /datum/data/pda/app/nanobank/proc/input_account_pin(mob/user)
 	var/attempt_pin = tgui_input_number(user, "Enter pin code", "NanoBank Account Auth", max_value = 99999)
-	if(!user_account || !attempt_pin)
+	if(!user_account || isnull(attempt_pin))
 		return
 	return attempt_pin