Fix rendering bug with saveLayerAlpha/drawColor.

drawColor() was not calling quickReject because it fills the clip region
and thus always passes the test. However, quickReject also checks whether
the current layer is invisible. drawColor() now performs the same check
and avoid drawing inside an invisible layer.

Change-Id: I63d0e9a8a9c0fba774f0f5c3870d58e6ed96fbd1