Fix an invalid use of ::back() on an newly emptied vector. Also tighten up several places where we never expect to have NULL pointers to assert early.
Fix an invalid use of ::back() on an newly emptied vector. Also tighten
up several places where we never expect to have NULL pointers to assert
early.

This fixes a valgrind error within CorrectTypo, but not the
non-determinism.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@134032 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang