ariya/phantomjs — pull request #12483 by zackw (2014-08-20 18:47:31+00:00)
Title: Fix crash on exit if pages have been closed (#12482)

Regression from #12431: the loop to clear all surviving pages
neglects to check for entries in `m_pages` which have already
been closed, fully destructed, and therefore replaced by NULL
pointers.