Don't try to call plug-in member functions if the plug-in hasn't been initialized
<rdar://problem/8730204>
Created attachment 76797 [details] Patch
Comment on attachment 76797 [details] Patch r=me
Committed r74205: <http://trac.webkit.org/changeset/74205>
http://trac.webkit.org/changeset/74205 might have broken Leopard Intel Debug (Tests)