Ensure moved-from container is cleared on move

In all cases except for this optimistic attempt to reuse memory, the
moved-from TinyPtrVector was left `empty()` at the end of this
assignment. Though using a container after it's been moved from can be a
bit sketchy, it's probably best to just be consistent here.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@320408 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed