[clang] Make sure codecompletion is called for calls even when inside a token.

Summary:
Currently CodeCompleteCall only gets called after a comma or parantheses. This
patch makes sure it is called even at the cases like:
```foo(1^);```

Reviewers: ilya-biryukov, ioeric, hokein

Reviewed By: ilya-biryukov

Subscribers: MaskRay, jkorous, arphaman, cfe-commits

Differential Revision: https://reviews.llvm.org/D51038

llvm-svn: 341824