The kernel can't handle umount /dev/hdc, we have to do it through mtab,

The kernel can't handle umount /dev/hdc, we have to do it through mtab,
except that we still have to work when there is no mtab.

Oh, and while we're at it, take advantage of the fact that modern processors
avoid branches via conditional assignment where possible.  ("x = a ? b : c;"
turns into "x = c; if (a) x = b;" because that way there's no branch to
potentially mispredict and thus never a bubble in the pipeline.  The if(a)
turns into an assembly test followed by a conditional assignment (rather
than a conditional jump).)  So since the compiler is going to do that _anyway_,
we might as well take advantage of it to produce a slightly smaller binary.

So there.