Don't call sinon.expectation.pass if there aren't any expectations.

This fixes an issue with sinon-qunit where sinon will create an empty
assertion if there aren't any expectations. In pure sinon where pass
doesn't do anything, the behavior will not change.

https://github.com/cjohansen/sinon-qunit/issues/10
Added test case
Merge pull request #513 from JeffreyFalgout/fix-mock-empty-verify

Don't call sinon.expectation.pass if there aren't any expectations.