If the user add APN with empty APN type, map it for default type

Original behavior will map all APN type if enter empty APN type. But it
sometimes cause problem that MMS or IMS not working when select to this
custom APN. So if the user doesn't enter any APN type, just map to
valure of carrier config 'apn_settings_default_apn_types_string_array'
to avoid all the functions broken.

Bug: 129704611
Test: 1.Enter empty APN type and check if only default is added into
APN. 2.atest ApnEditorTest pass.
Change-Id: Icec274e5b402af06822479bcc60294b347f5254f