`OrderBook._remove()` doesn't update `index.length` properly.

Summary

OrderBook._remove() doesn't update index.length properly.

OrderBook._remove() doesn't update index.length properly.

OrderBook._remove() is used to remove the existing order from the tree and index.length should be 0 when the original tree is empty.

index.length = index.length > 0 ? index.length - 1 : 1;

OrderBook._remove() updates index.length wrongly and _length() will return the wrong result.

Manual Review

We should change this line like below.

index.length = index.length > 0 ? index.length - 1 : 0;