ViewGroup: Fix dispatching of generic motion events

The change I58a9c06b7651ebe97cd03447b083cc9887f863b1
introduced a self-apparent bug. We fix it and amend the test case so
that the issue would have been caught.

Bug: 281951190
Test: atest ViewGroupTest
Change-Id: I886a2594a091e5d1870e564b67d46ce5e4901ae5
Merged-In: I886a2594a091e5d1870e564b67d46ce5e4901ae5