Move WebPopupMenuImpl::initialize m_client check
Move WebPopupMenuImpl::initialize m_client check

This should be checked in case the page is closed before it's created.

TBR=jbauman@chromium.org

Review URL: https://codereview.chromium.org/301183007

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@175310 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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