Add some extra checks to the MoveOnly test class to ensure it is not constructed or assigned from in a moved-from state.

Some tests were constructing it with 0, so use -1 as the invalid state
instead.

Reviewers: Marshall Clow

Differential Revision: http://reviews.llvm.org/D4095

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@215301 91177308-0d34-0410-b5e6-96231b3b80d8