[Mac] Puts a NULL check in case a native plugin library cannot be loaded (.dll on mac, for example).
[Mac] Puts a NULL check in case a native plugin library cannot be loaded (.dll on mac, for example).

TEST=Load an extension that requires a .dll or other platform-specific file and make sure it does not crash the browser.
BUG=29584
Review URL: http://codereview.chromium.org/492012

git-svn-id: http://src.chromium.org/svn/trunk/src@34308 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 477359f25a491e81a60a5cb0d177066420578e62
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser