.c_str() on an empty localized string returns NULL/nullptr

[bradcray]

When using c_str() on a .localize()d empty string, we seem to get NULL out rather than an empty string (ATO). For example, the following program:

use CTypes, IO, IO.FormattedIO;

extern proc printf(fmt...);

var emptyStr: string = "";
var aStr: string = "a";

printf("%d %s %s\n", here.id, aStr.c_str(), emptyStr.c_str());
for loc in Locales do on loc {
  printf("%d %s %s\n", here.id, aStr.localize().c_str(), emptyStr.localize().c_str());
}

prints:

0 a
0 a (null)
1 a (null)

where the lines after the first indicate a bad interaction between c_str() and localize() (or more likely, a bug in localize()).