Addition of buffer ID parameter on bindFrameBuffer

After rendering to texture on iOS, it is necessary switch back to the default buffer which generally not 0/null. As such the frame buffer id needs to be provided so it can be set correctly. To establish the correct framebuffer id to switch back too, use 

screenBufferId = GL.getParameter(GL.FRAMEBUFFER_BINDING);

prior to binding the framebuffer for the RTT.