Web Inspector: Exception in timeline DOMCounters
https://bugs.webkit.org/show_bug.cgi?id=112427

Reviewed by Pavel Feldman.

Do not update marker on DOM counters graph if the graphs haven't been
drawn yet.

* inspector/front-end/MemoryStatistics.js:
(WebInspector.MemoryStatistics.prototype._refreshCurrentValues):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@146047 268f45cc-cd09-0410-ab3c-d52691b4dbfc