core/load-fragment: don't treat "; ;" as "/usr/bin/;"

core/load-fragment: don't treat "; ;" as "/usr/bin/;"

We had a special test case that the second semicolon would be interpreted
as an executable name. We would then try to find the executable and rely
on ";" not being found to cause ENOEXEC to be returned. I think that's just
crazy. Let's treat the second semicolon as a separator and ignore the
whole thing as we would whitespace.