getSliceChunkFile and checkChunkSize may be not match

[zengxiaobai]

code in getContents like:
	fromByte := uint64(reqChunks[from] * uint32(c.md.BlockSize))
	if index < len(availableChunks) {
		chunkFile, _ := getSliceChunkFile(c, availableChunks[index])
		if chunkFile != nil {
			if err := checkChunkSize(c, chunkFile, idx); err != nil {
				_ = chunkFile.Close()
				_ = c.bucket.Discard(context.Background(), c.id)
				return nil, 0, err
			}


chunkFile, _ := getSliceChunkFile(c, availableChunks[index]
 checkChunkSize(c, chunkFile, idx)

the question is here:
chunkFile, _ := getSliceChunkFile(c, availableChunks[index]) if chunkFile != nil { if err := checkChunkSize(c, chunkFile, idx
idx != availableChunks[index]