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

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@312028 91177308-0d34-0410-b5e6-96231b3b80d8

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