[llvm-rc] Fix DIALOG(EX) parsing ability (parser, pt 5/8).

This fixes a use-after-free bug that was noticed by a sanitizer buildbot
(http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fast/builds/7502).

Differential Revision: https://reviews.llvm.org/D37271

llvm-svn: 312028