clang-format: Fix crasher.

Caused by unknown tokens (e.g. "\n") not properly updating the state.

Example:
  const char* c = STRINGIFY(
  \na : b);

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203645 91177308-0d34-0410-b5e6-96231b3b80d8