Please remove 'while True' from 'work_out_row()' function

[mako101]

https://github.com/cutajarj/multithreadinginpython/blob/b2df1e8420c1051f6899a4a1fbdbecf62b6c0136/barriers/matrix_multiply.py#L20

This loop causes the barrier.wait() to be called too many times, which i think resets the count when it reaches 0 and therefore the code never exits