Fix APN cannot save after ApnEditor is paused.

When ApnEditor is paused and user does not enter name or APN,
the new APN URI will be deleted in validateAndSave() method.
After the activity is resumed, the APN will not able to be
saved because the database record has been deleted.

Change-Id: I19f5246020e4a52239a7fc0ac86a281372e34b90