Bug Report, lac.run() changed input text_list

```python
lac = LAC(mode='lac')
text1 = ['', 'a']
text2 = ['', 'a']
print(text1==text2)
res = lac.run(text1)
print(text1==text2)
```

> True
> False

Seem that lac.run changed the input text where it shouldn't be.
That will happen when an empty string in the input list.
Should we use deepcopy() to avoid modifying input if we must modify something?

Start by running the reported lac.run() example with an input list containing an empty string and inspect the Python implementation behind that entry point. The fix is done when lac.run() no longer changes the caller's input list, with a regression test covering this case.

Written by the indexing model from the issue text.