avoid stopping app in case of accessing empty db

When accessing empty database, Setting App is stopped, sometimes.
To avoid stopping app, check null for cursor

Change-Id: I71ec067f502d12a9215a9abdbe9e23fc07af17bb

src/com/android/settings/ApnSettings.java

@@ -164,6 +164,7 @@ public class ApnSettings extends PreferenceActivity implements
                 "_id", "name", "apn", "type"}, where, null,
                 Telephony.Carriers.DEFAULT_SORT_ORDER);
 
+        if (cursor != null) {
             PreferenceGroup apnList = (PreferenceGroup) findPreference("apn_list");
             apnList.removeAll();
 
@@ -203,6 +204,7 @@ public class ApnSettings extends PreferenceActivity implements
                 apnList.addPreference(preference);
             }
         }
+    }
 
     @Override
     public boolean onCreateOptionsMenu(Menu menu) {