Fixes multiple formatting bugs.

Fixes:
- incorrect handling of multiple consecutive preprocessor directives
- crash when trying to right align the escpaed newline for a line that
  is longer than the column limit
- using only ColumnLimit-1 columns when layouting with escaped newlines
  inside preprocessor directives

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171401 91177308-0d34-0410-b5e6-96231b3b80d8