GTK: fix navigation button click logic.
GTK: fix navigation button click logic.

BUG=none
TEST=right click on new tab button should do nothing rather than crash in debug.

Review URL: http://codereview.chromium.org/3005014

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@52782 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