blast: default to surface damage to invalid

SurfaceDamage should be invalid unless set. Invalid SurfaceDamage
forces HWC to assume the whole buffer is damaged. Clearing the
damage tells HWC the buffer hasn't changed at all.

Bug: 139311175
Test: Repro steps in https://b.corp.google.com/issues/139311175#comment1
Change-Id: Ifcb84d8a974994c8d5204c34933b4b3390f13af5