Fix null pointer exceptions in NetworkPolicyEditor

This upload fixes a null pointer exception issue.
After this fix the modified methods return
their corresponding default values instead of null.
Cherry-picked from AOSP: https://android-review.googlesource.com/#/c/62248/

Change-Id: Idb94f8b808b8dd18be5e3fc92cc5560ce0f81c4f
Show memory full text only for internal storage

When the internal memory is full, a warning text is shown
in Settings/Storage. This warning was displayed for all
types of memory (internal/primary, sd card and usb storage)
even though it was only referring to the primary memory.
With this fix, it is only shown for the primary memory.

Change-Id: I35ad4b0b45c6752ddc9d7166495435b27fd4a170
Bleed keyguard widget picker list into translucent bars

Change-Id: Ie929845fd8b822dcf858b9b56cb5758379d55c59
Remove empty App Security preference group

Change-Id: Ia36eeed8b0d38c826ed499b5fd2b8264f45a459f