clang-format: Be slightly more cautious when formatting subsequent lines after...

clang-format: Be slightly more cautious when formatting subsequent lines after a change. With r251474, clang-format could indent the entire rest of the file, if there is a missing closing brace, e.g. while writing code in an editor.

Summary:
With this change, clang-format stops formatting when either it leaves
the current scope or when it comes back to the initial scope after
going into a nested one.

Reviewers: klimek

Subscribers: cfe-commits, klimek

Differential Revision: http://reviews.llvm.org/D14213

llvm-svn: 251760