[Issue 19691] ICE on null default value for struct parameter in constructor

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19691

--- Comment #3 from Basile-z <b2.temp at gmx.com> ---
The reduction is actually slightly different. With the upcoming fix the initial
test case will pass an fall back on the string overload (even if with a dep
message) but the reduction will fail.

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