there is a crash in dbscan algoritm

in my data, row 26th will run into https://github.com/sjwhitworth/golearn/blob/74ae077eafb245fa3bdca0288854b6d51f97fe60/clustering/dbscan.go#LL122C4-L122C4 and bit 277 will write into clustered, and row 277 will run into https://github.com/sjwhitworth/golearn/blob/74ae077eafb245fa3bdca0288854b6d51f97fe60/clustering/dbscan.go#L74 because row 277 has been in clustered but has not been in visited, and then crash