Fix safety issue -- freebsd core dump?

[Steven Schveighoffer]

I submitted a fix [1] for a safety issue that I found [2]

However, FreeBSD 64-bit is core dumping when testing the compiler [3]. 
It seems consistent, but also seems like it doesn't make sense for that 
change to cause that, and only on one platform.

Any idea how to find out why it's core dumping, aside from installing a 
FreeBSD system?

-Steve

[1] https://github.com/dlang/druntime/pull/3185
[2] https://issues.dlang.org/show_bug.cgi?id=21116
[3] 
https://auto-tester.puremagic.com/pull-history.ghtml?projectid=1&repoid=2&pullid=3185