fix regression in #20863 triggering an assertion if TypeInfo_AssociativeArray is misdefined

[rainers]

Fail gracefully with empty declaration.

[dlang-bot]

Thanks for your pull request, @rainers!

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dub run digger -- build "master + dmd#22126"

[schveiguy]

If it passes CI, probably good.

[ibuclaw]

Judging from the errors, this ought to be at the top of the visit method.

    override void visit(TypeInfoAssociativeArrayDeclaration ti)
    {
        if (ti.semanticRun >= PASS.semantic3)
            return;
        ti.semanticRun = PASS.semantic3;

[rainers]

Judging from the errors, this ought to be at the top of the visit method.

Good point, added.

[ibuclaw]

I've just realised that this will still trigger an assert and ICE if druntime is seriously mismatched with the compiler by declaring these fields but of a different type.

class TypeInfo_AssociativeArray
{
    alias aaOpEqual(K, V) = () => false;
    alias aaGetHash(K, V) = () => 0;
}

[ibuclaw]

#22143