Prevent NFE in SystemUI when parsing invalid int

A user can change the sysui_rounded_content_padding setting via adb.

If the value set is not an integer, SystemUI will end up in an exception
loop.

Bug: 117152006
Test: No crash when running:
      adb exec-out settings put secure sysui_rounded_content_padding a
Change-Id: I49cace6087effae20170eab9175fc84ebcd21781