get_item with lazy expressions containing reductions fails to index properly

[lshaw8317]

The code below

a = blosc2.linspace(0, 10, num=100, shape=(10, 10))
le = blosc2.lazyexpr("sum(a, axis=0)", {'a': a})
print(le[3])

returns the whole array, not just the fourth element. This seems to occur with any reduction.