fix transitions from hwc to GLES composition

If we switched from HWC to GLES but the dirty region was empty
(could happen if the dirty region is outside of the screen for instance), we
need to force a full screen composition.

In this change we ignore the dirty region for the purpose of
rejecting the whole update and we rely on the fact that it will later
be expanded to the whole screen. This was the least risky fix.

Bug: 7467760, 7452931
Change-Id: I2132f2f963b00a3ce7150adadb107b0367b3862e