DSLX type checker should not error on width slice of 0-bit value

[mikex-oss]

Describe the bug
The following code does not compile, even though we'd expect to "skip the loop" for N == 0.

fn foo<N: u32>(x: uN[N]) {
    for (idx, _): (u32, ()) in range(u32:0, N) {
        trace_fmt!("{}", x[idx+:u1]);
    }(())
}

fn main() { foo(uN[0]:0); }

0020:         trace_fmt!("{}", x[idx+:u1]);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^-^ XlsTypeError: uN[0] vs uN[1]: Slice type must have <= original number of bits; attempted slice from 0 to 1 bits.

You cannot get around this with x[idx:idx + 1] or special casing if N == u32:0 ... inside the function (inside or outside the loop).

Note that the array version does work (though runs into IR conversion issues - #917).

fn foo<N: u32>(x: u1[N]) {
    for (idx, _): (u32, ()) in range(u32:0, N) {
        trace_fmt!("{}", x[idx]);
    }(())
}

fn main() { foo(u1[0]:[]); }

To Reproduce
Compile the code above.

Expected behavior
There should be a way for this to type check since other parts of XLS allow the 0-bit type.