Occasionally we'll receive the stylus up signal (pressure = 0) before
we receive the touch screen up signal. Rather than giving pointer a
pressure value of 0 (which is one of the signals of hovering) or
falling back to the touchscreen pressure values (which would make for
an inconsistent stream), use the previous pressure value which should
always be non-zero for a stream of fused data.
Bug: 20449776
Change-Id: I71eb97e7c4ea53e42b0eb54fc1f8ae7f89aad9d1
53dca3aadd