fix(chat-character-image): 캐릭터 이미지 트리거 수정

- triggers가 null이거나 빈 리스트이면 수정없이 실행종료

src/main/kotlin/kr/co/vividnext/sodalive/admin/chat/character/image/AdminCharacterImageController.kt

@@ -94,7 +94,9 @@ class AdminCharacterImageController(
         @PathVariable imageId: Long,
         @RequestBody request: UpdateCharacterImageTriggersRequest
     ) = run {
-        imageService.updateTriggers(imageId, request.triggers ?: emptyList())
+        if (!request.triggers.isNullOrEmpty()) {
+            imageService.updateTriggers(imageId, request.triggers)
+        }
 
         ApiResponse.ok(null)
     }