fix: 기존 캐릭터에 폴더 추가 안되는 것 수정 (#779)

existing character chat folder

# PR Checklist
- [ ] Have you checked if it works normally in all models? *Ignore this
if it doesn't use models.*
- [ ] Have you checked if it works normally in all web, local, and node
hosted versions? If it doesn't, have you blocked it in those versions?
- [ ] Have you added type definitions?

# Description
기존 캐릭터에 폴더 추가 안되는 것을 수정하는 PR입니다.

src/lib/SideBars/SideChatList.svelte

@@ -479,6 +479,9 @@
                 <SplitIcon size={18}/>
             </button>
             <button class="ml-auto text-textcolor2 hover:text-green-500 mr-2 cursor-pointer" onclick={() => {
+                if (!chara.chatFolders) {
+                    chara.chatFolders = []
+                }
                 const folders = chara.chatFolders
                 const length = chara.chatFolders.length
                 folders.unshift({