Fix bug when extract multiple adjacent words from a string without word boundaries

[lishukan]

Dear developers： There is no doubt that flashtext is an excellent string matching tool. I have already used it on a large number of occasions. But recently I found it in a string without word boundaries (such as a Chinese sentence),

If two words that need to be extracted happen to be adjacent, then it will only be able to extract the first word.

So I made some modifications: when matching words, the index for the next iteration will start at the end of the last matched word.

I have added a new use case and It passed all unit tests.

[abulice]

邮件已收到。

[lishukan]

@vi3k6i5 Hello, dear owner . Is this repo still maintained ？ I found that this repo hasn't updated its code for a long time . If it is no longer maintained, I will no longer wait for the merge of the MR.