Skip ensure return check when ensure has no body

[eitoball]

This PR should fix a case that Lint::EnsureReturn throws an exception when ensure clause has no body like

begin
  something
ensure
end

[bbatsov]

Looks good. Please, add an entry about the bugfix in the Changelog.

[coveralls]

Coverage increased (+0%) when pulling 2d1655aaf82675e5184d1a19c7531546ce3f5407 on eitoball:skip_check_when_ensure_has_no_body into 09b0571 on bbatsov:master.

[eitoball]

Looks good. Please, add an entry about the bugfix in the Changelog.

Thank you for checking out. Is 4e0fd65 okay?

[bbatsov]

Yep, it's great. Please, squash the two commits into one rebasing on top of the current master and I'll have the PR merged.

[eitoball]

Yep, it's great. Please, squash the two commits into one rebasing on top of the current master and I'll have the PR merged.

Done.

[coveralls]

Coverage remained the same when pulling 9a6cd9f on eitoball:skip_check_when_ensure_has_no_body into d8026cf on bbatsov:master.

[bbatsov]

Thanks!