Document record mixing mail swap

src/item_use.c

@@ -182,7 +182,7 @@ u8 CheckIfItemIsTMHMOrEvolutionStone(u16 itemId)
 // Mail in the bag menu can't have a message but it can be checked (view the mail background, no message)
 static void CB2_CheckMail(void)
 {
-    struct MailStruct mail;
+    struct Mail mail;
     mail.itemId = gSpecialVar_ItemId;
     ReadMail(&mail, CB2_ReturnToBagMenuPocket, 0);
 }