Refactor 'lastcharmessage' cbs (#554)

# PR Checklist
- [ ] Did you check if it works normally in all models? *ignore this
when it dosen't uses models*
- [ ] Did you check if it works normally in all of web, local and node
hosted versions? if it dosen't, did you blocked it in those versions?
- [ ] Did you added a type def?

# Description
While implementing a specific behavior through CBS, I encountered
limitations during handling first message. Therefore, I aim to modify
the effect of certain keywords to accommodate a broader range of cases.
The changes have been tested and presented no issues. However, I kindly
request your review from a structural design perspective to ensure
adequacy.

src/ts/parser.ts

@@ -590,19 +590,16 @@ function basicMatcher (p1:string,matcherArg:matcherArg,vars:{[key:string]:string
         switch(lowerCased){
             case 'previous_char_chat':
             case 'lastcharmessage':{
-                if(chatID !== -1){
-                    const selchar = db.characters[get(selectedCharID)]
-                    const chat = selchar.chats[selchar.chatPage]
-                    let pointer = chatID - 1
-                    while(pointer >= 0){
-                        if(chat.message[pointer].role === 'char'){
-                            return chat.message[pointer].data
-                        }
-                        pointer--
+                const selchar = db.characters[get(selectedCharID)]
+                const chat = selchar.chats[selchar.chatPage]
+                let pointer = chatID !== -1 ? chatID - 1 : chat.message.length - 1
+                while(pointer >= 0){
+                    if(chat.message[pointer].role === 'char'){
+                        return chat.message[pointer].data
                     }
-                    return selchar.firstMsgIndex === -1 ? selchar.firstMessage : selchar.alternateGreetings[selchar.firstMsgIndex]
+                    pointer--
                 }
-                return ''
+                return selchar.firstMsgIndex === -1 ? selchar.firstMessage : selchar.alternateGreetings[selchar.firstMsgIndex]
             }
             case 'previous_user_chat':
             case 'lastusermessage':{