Check for null pkgList in fixSeInfoLocked()

Addresses:
03-08 17:26:18.550 11945 11945 E AndroidRuntime: *** FATAL EXCEPTION IN SYSTEM PROCESS: main
03-08 17:26:18.550 11945 11945 E AndroidRuntime: java.lang.NullPointerException: Attempt to invoke interface method 'java.util.Iterator java.util.List.iterator()' on a null object reference
03-08 17:26:18.550 11945 11945 E AndroidRuntime:        at com.android.server.pm.SharedUserSetting.fixSeInfoLocked(SharedUserSetting.java:129)

Which is triggered during an "adb sync"

Fixes: 74214574
Test: m -j && adb shell stop && adb remount && adb sync && adb shell start
Change-Id: I1908893fae05c70491f7cc776d0df49ec54f283b