[Qt] REGRESSION(r141240) Crash in PluginPackage::fetchInfo
https://bugs.webkit.org/show_bug.cgi?id=111322

Reviewed by Simon Hausmann.

Do not try to load blacklisted plugins.

* plugins/qt/PluginPackageQt.cpp:
(WebCore::PluginPackage::fetchInfo):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144627 268f45cc-cd09-0410-ab3c-d52691b4dbfc