Fix preference grouping in SettingsPreferenceGroupAdapter

When expand button is not expanded (when it's not expanded, its
getOrder() will return 999), we should treat this as a part of the
previous group and should not start a new group when calculating the
round corner.

Bug: 418260806
Test: Manual
Flag: EXEMPT bugfix
Change-Id: Ic7d7002a1913ddd2c04494e3817c094b00a15d23