MakerDAO Liquidations 2.0

There is no check that enforces the price returned by `pip.peek()` be greater than zero inside `Clipper.kick` and `Clipper.redo`. This would lead to setting the `top` value of an auction to zero, which is probably not desired. Having `top == 0` would cause a revert in the `rdiv(price, top)` inside the `Clipper.status` function, which would block access to calling `Clipper.redo` and `Clipper.take` again for `tail` amount of seconds.

There is a primitive division operation inside the `bark` function which could lead to a “division by zero” error, because the divisor is not checked to be greater than zero, i.e. the 2nd division on L174: `dart = min(art, mul(room, WAD) / rate / milk.chop);` where `milk.chop` could be zero if set by the `Dog.file` function.