fix test case wrap_row_5, the last row was ignored

[haoyu234]

https://github.com/randrew/layout/blob/b0c02829df41b066c5aaedcb946498209bcb38e5/layout.h#L982-L983 According to the original annotation, the last line does not seem to do justify, my modification destroys this behavior

This change has passed all test cases, and it is not known if it will affect other projects