[SymbolFilePDB] Remove a few null pointer checks by passing ref

Reviewers: zturner, rnk, lldb-commits

Reviewed By: zturner

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D44455

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@327908 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed