BUG: wrong selection for orders falling into equal ranges

when orders are selected where the kth element falls into an equal range
the the last stored pivot was not the kth element, this leads to losing
the ordering of smaller orders as following selection steps can start at
index 0 again instead of the at the offset of the last selection.
Closes gh-4836
Merge pull request #4837 from juliantaylor/select-bug

BUG: wrong selection for orders falling into equal ranges