fix for NPE
05-02 16:27:48.084 E/AndroidRuntime(10933): java.lang.NullPointerException
05-02 16:27:48.084 E/AndroidRuntime(10933): at com.android.deskclock.worldclock.AddCityDialog.checkSelectionStatus(AddCityDialog.java:322)
05-02 16:27:48.084 E/AndroidRuntime(10933): at com.android.deskclock.worldclock.AddCityDialog.setTimeZoneData(AddCityDialog.java:275)
05-02 16:27:48.084 E/AndroidRuntime(10933): at com.android.deskclock.worldclock.AddCityDialog.onPostExecute(AddCityDialog.java:113)
05-02 16:27:48.084 E/AndroidRuntime(10933): at com.android.deskclock.worldclock.AddCityDialog.onPostExecute(AddCityDialog.java:81)

Change-Id: I261f4f9a9ad54a1965cb37fe612e806994a30f67