Cast converts AA to rvalue?

[Johan]

Testcase:
```
shared int[int] aa;
void main () {
     cast()aa[1] = 1;
}
```

Up to dlang 2.097, this program runs and works fine.
Since dlang 2.098, the program errors with:
`core.exception.RangeError@/app/example.d(3): Range violation`

I think the 2.098+ behavior is correct, but I cannot find 
anything about the change of this language behavior in the 
release notes.

Please enlighten me,
   Johan

related discussion: 
https://forum.dlang.org/post/etxuhqzlkofitxswsxel@forum.dlang.org