fix issue 3490 - DMD Never Inlines Functions that Could Throw

Note: The issues the original bug reporter had with std.range and enforce have already been addressed at least several versions ago. See my ("Nick Sabalausky") comment in [issue 3490] (https://d.puremagic.com/issues/show_bug.cgi?id=3490#c5).

This turned out to be pretty simple and straightforward, so I'm hoping that doesn't mean I've overlooked anything important. But it worked when I tried it and checked the disassembly.