[Issue 24018] array concatenation doesn't work with disabled default construction

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24018

--- Comment #1 from FeepingCreature <default_357-line at yahoo.de> ---
I think the underlying problem is maybe actually that `.length =` does default
construction. There is no way to change length at once without "constructing"
the target memory, but that's what `_d_arraycatnTX` requires.

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