Fixed crash related to cellular network payment plan retreival.

BUG=chromium-os:8864
TEST=none

Review URL: http://codereview.chromium.org/4690002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@65405 0039d316-1c4b-4281-b951-d872f2087c98
  virtual const Network* active_network() const {
    if (ethernet_ && ethernet_->is_active())
      return ethernet_;
    if (wifi_ && wifi_->is_active())
      return wifi_;
    if (cellular_ && cellular_->is_active())
      return cellular_;
    return NULL;
  }

  virtual const Network* active_network() const {
    if (ethernet_ && ethernet_->is_active())
      return ethernet_;
    if (wifi_ && wifi_->is_active())
      return wifi_;
    if (cellular_ && cellular_->is_active())
      return cellular_;
    return NULL;
  }
