Fix a crashing bug (dart-lang/pub_semver#19)

VersionRange.difference() with a VersionUnion didn't expect to get an
empty constraint, but it was possible to do so.

Closes dart-lang/pub_semver#18
4 files changed
tree: 6d4331496018ccc70d68e5894d8dd7b451e19127
  1. pkgs/