When placing an annotation token over an existing annotation token, make sure...

When placing an annotation token over an existing annotation token, make sure that the new token's range extends to the end of the old token. Assert that in AnnotateCachedTokens. Fixes PR6248.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@95555 91177308-0d34-0410-b5e6-96231b3b80d8