Fix no ringtone and notification sound after MediaScan

When ringtone and notification is not customized, the customized
ringtone/notification file name will be null. It will lead to
NullPointer exception when call doesPathHaveFilename().
Fix it by adding customize feature control and empty check.

CRs-Fixed: 754038

Change-Id: Ife7e041acbeec2c7da976da8d32b22c60f52a70c