Correctly indent with tabs when whitespace starts from the column not divisible by TabWidth.

Summary:
The width of the first inserted tab character depends on the initial
column, so we need to handle the first tab in a special manner.

Reviewers: klimek, djasper

Reviewed By: klimek

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1763

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@191497 91177308-0d34-0410-b5e6-96231b3b80d8