Do not traverse the break-state when we know we cannot break anyway.

This is an optimization that djasper spottet. For now, we do not format
anything after the first token that belongs to such an implicit string
literal. All our state is not made for handling that anyway, so we'll
revisit this if we find a problem.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172537 91177308-0d34-0410-b5e6-96231b3b80d8