[fix] host일 때 방에 참가하는 로직 건너 뛰도록 수정

src/main/java/org/sopt/sweet/domain/room/service/RoomService.java

@@ -90,10 +90,20 @@ public RoomInviteResponseDto getRoomInviteInfo(String invitationCode) {
     public JoinRoomResponseDto findAndJoinRoom(Long memberId, String invitationCode) {
         Member member = findMemberByIdOrThrow(memberId);
         Room room = findByInvitationOrThrow(invitationCode);
-        joinRoom(member, room);
+        if (!isOwner(memberId, room.getId())) {
+            joinRoom(member, room);
+        }
         return JoinRoomResponseDto.of(room.getId());
     }
 
+    public Boolean isOwner(Long memberId, Long roomId) {
+        Optional<Member> member = memberRepository.findById(memberId);
+        Optional<Room> room = roomRepository.findById(roomId);
+        Boolean isOwner = member.get().getId().equals(room.get().getHost().getId());
+        return isOwner;
+    }
+
+
     @Transactional(readOnly = true)
     public RoomMainResponseDto getRoomMainInfo(Long memberId, Long roomId) {
         Member member = findMemberByIdOrThrow(memberId);