[HOTFIX] JoinRoom에서 상대방 ImageIndex 반환하도록 수정

socket/handlers/matchmaking.js

@@ -65,6 +65,7 @@ module.exports = function(io, socket, gameState) {
                 roomId: roomId,
                 opponentRating: gameState.playerRating.get(matchedRoom.hostId),
                 opponentNickname: gameState.nickname.get(matchedRoom.hostId),
+                opponentImageIndex: gameState.imageIndex.get(matchedRoom.hostId),
                 isBlack: !isHostFirst
             });