Divide by zero error

[jcobol]

It is possible for a token counter to return zero tokens, leading to a division by zero error in the merge_splits function:

  File "C:\Users\user\miniconda3\envs\project\Lib\site-packages\semchunk\semchunk.py", line 78, in merge_splits
    average = cumulative_lengths[midpoint] / tokens if cumulative_lengths[midpoint] else average
              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~
ZeroDivisionError: division by zero

[umarbutler]

Thanks for this! This bug is now fixed in v0.3.2 :)