Draw in the correct FBO after invoking a GL functor

Bug #5650514

After invoking a GL functor, libhwui restores a few OpenGL states
including the current FBO. The renderer was however making the
wrong assumption that the FBO to restore to was the base layer
instead of the FBO associated with the current canvas state.

Change-Id: Ie565500832ebffd673f6a43b83422d6cc05470a0