[Issue 24064] New: Cannot chain() array and immutable Nullable

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24064

          Issue ID: 24064
           Summary: Cannot chain() array and immutable Nullable
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: regression
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: elpenguino+D at gmail.com

```
immutable Nullable!string foo = "b";
string[] bar = ["a"];
assert(chain(bar, foo).equal(["a", "b"]));
```
Before DMD 2.105.0, this code ran successfully. Regression appears to be caused
by 
https://github.com/dlang/phobos/commit/b9c6e3ca4b6fec799964394ad3e080d7b347f658.

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