Fix ranges computed by git clang-format.

Before, the computed byte range would include the trailing newline.
clang-format on the other hand counts whitespace as belonging to the
following token, so that git-clang-format inadvertendly reformats the
first unmodified line as well.

It is not entirely clear whether clang-format's behavior itself should
be modified, but for now this seems to be a safe change.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@185423 91177308-0d34-0410-b5e6-96231b3b80d8