SF: do not latch unsignaled in early offsets

When we are in early offsets we are most likely in client composition
and/or WM animating windows. Avoid latching unsignaled buffers in this
case to avoid jank when an unsignaled buffers block newer transactions
from getting applied in the next frame.

Bug: 205153280
Test: modified TouchLatency app with long draws
Change-Id: Ice5456db1dec1feaf11f6e022a1eaaedfb26781f