Incorrect behavior of itertools::product for empty range argument

[Wentzell]

Description

When one of the ranges passed to itertools::product is an empty range, the resulting product range should be empty.
Currently this is not the case.

Steps to Reproduce

This test currently fails

long count = 0;
for (auto [l, m] : product_range(0, 5)) ++count;
EXPECT_EQ(count, 0);

Versions

d10e86d