Copy virtual display FB to outbuf even with no app layers

In the current composition strategy we bail out if there are no app
layers present. However, this leads to undesirable behaviour if the
FB contains valid data that is expected as output. In this patch we
copy the FB to the output buffer to satisfy this use case.

Change-Id: If905d8b0652faf73b9aecad1abc760f21967807f
1 file changed