Reset plugin group version to "0" instead of NULL.
Reset plugin group version to "0" instead of NULL.

This guards against dereferencing NULL when the group is empty.

BUG=72946
TEST=PluginGroupTest.*

Review URL: http://codereview.chromium.org/6532024

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@75270 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser