linux: avoid closing uninitialized resolver
linux: avoid closing uninitialized resolver

When _res is uninitialized, res_nclose may end up closing fd 0.
Test whether it's initialized before closing.

Patch by Jim Deng <jdeng@google.com>.

TEST=chrome without a net connection doesn't crash on startup

Review URL: http://codereview.chromium.org/3717002

git-svn-id: http://src.chromium.org/svn/trunk/src@62288 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 74c6f31123bebeb0a7cf70dcb29912fdf0e2bafe
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