base: check also for mLayoutParams before calling checkForRelayout

http://jira.omnirom.org/browse/OMNI-976

This was introduced with
https://github.com/omnirom/android_frameworks_base/commit/b3670c54e60387fde633fb91c649c5b896f8b962

Change-Id: I06c1926c5b8102b336d128d9b411f74a9eff3ded
Delete duplicate SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION flag

AOSP gerrit: https://android-review.googlesource.com/#/c/96374/