Strange appender behavior

[tchaloupka]

Is this expected?:

```
import std.stdio;
import std.algorithm;
import std.array;

void main()
{
     auto d = Appender!string();
     //auto d = appender!string(); // works

     string[] arr = ["foo", "bar", "baz"];
     arr.joiner("\n").copy(d);
     writeln(d.data);
}
```

Using Appender outpust nothing, using appender works ok.