BUG: fix fancy indexing with negated strides

When strides where negated and the subspace had a size of 1, then
finding the output array strides did not work because
DONT_NEGATE_STRIDES was not set on the iterator used to find
the output arrays strides.
Merge pull request #4553 from seberg/fancy-negated-strides

BUG: fix fancy indexing with negated strides