Only run KDE browser fallback when necessary

Otherwise, in some circumstances, read_kde_browser incorrectly prints the result twice.

BUG=33842
TEST=xdg-settings get default-web-browser should not output two files when kdeglobals contains a BrowserApplication[$*] entry
Review URL: http://codereview.chromium.org/3330004

git-svn-id: http://src.chromium.org/svn/trunk/deps/third_party/xdg-utils@58316 4ff67af0-8c30-449e-8e8b-ad334ec8d88c
2 files changed