Ignore submodules with an empty url.
Ignore submodules with an empty url.

Review URL: https://chromiumcodereview.appspot.com/10850028

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@149752 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build