Remove an unnecessary check for FormatTok not being null.

Summary:
This check hints clang analyzer, that FormatTok may be null, and it
reports a null pointer dereference error:
http://buildd-clang.debian.net/scan-build/report-827c64.html#Path28

Reviewers: djasper

Reviewed By: djasper

CC: cfe-commits, klimek

Differential Revision: http://llvm-reviews.chandlerc.com/D3040

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203800 91177308-0d34-0410-b5e6-96231b3b80d8