Fixed a Settings crash.

+ When in Settings->More... we will no longer provide a tethering option
if tethering requires provisioning, but the provisioning app is invalid.

Bug: 17671381
Change-Id: I48a8178865a7ffddec714c1f6ee6f18d34801b60

src/com/android/settings/WirelessSettings.java

@@ -367,6 +367,10 @@ public class WirelessSettings extends SettingsPreferenceFragment
         } else {
             Preference p = findPreference(KEY_TETHER_SETTINGS);
             p.setTitle(Utils.getTetheringLabel(cm));
+
+            // Grey out if provisioning is not available.
+            p.setEnabled(!TetherSettings
+                    .isProvisioningNeededButUnavailable(getActivity()));
         }
 
         // Enable link to CMAS app settings depending on the value in config.xml.