[clang-tidy] TwineLocalCheck: add param # checking

Summary:
The statement **getArg** tries to get the first one without checking, which may cause segmentation fault.

 

Reviewers: chh, bkramer

Reviewed By: bkramer

Subscribers: cfe-commits, xazax.hun

Tags: #clang-tools-extra

Differential Revision: https://reviews.llvm.org/D33103

llvm-svn: 303001