Fix the use of unitialized value while reporting double free in ASAN.

Summary:
This is a follow up to https://reviews.llvm.org/rL280201 where this issue was introduced.

ASAN tests failed:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux/builds/25219/steps/run%20asan%20tests/logs/stdio

Reviewers: filcab

Subscribers: kubabrecka

Differential Revision: https://reviews.llvm.org/D24109

llvm-svn: 280325