Summary: Fix suggested by @mclow.lists on D8109. Store the size of the un-poisoned vector upon construction instead of calculating it later.
Reviewers: titus, mclow.lists, kcc, EricWF
Reviewed By: EricWF
Subscribers: mclow.lists, cfe-commits
Differential Revision: http://reviews.llvm.org/D8172
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@231729 91177308-0d34-0410-b5e6-96231b3b80d8