shadowed label false positive in closure

[durka]

It seems that #27093 did not fully fix #25343. The following code reports a spurious warning on 'b:

'a: loop { break; }
'b: loop { break; }

// no warning
fn does_not_shadow() {
    'a: loop {}
}

// false positive
let also_does_not_shadow = || {
    'b: loop {}
};

Stable, beta, nightly.