Handle zero-length input

[ms609]

Thanks for this handy package.

It would be useful to add a sense check to avoid crashing R when a zero-length input is provided.

RcppHungarian::HungarianSolver(matrix(0, 0, 0)) # Crashes R

One alternative would be to return an error, but I've proposed returning a zero-length, zero-score matching.

I've not checked or tested the code proposed below, but hopefully it provides a useful starting point.

[jan-glx]

Great! The second element of the returned list should be 2 column 0 row matrix though.

[ms609]

I've updated the proposed code accordingly.