[3.0] Fix for FrameBufferImage.
* The Connect() and Disconnect() methods are unnecessarily
implementing a counter that tracks how many handlers are
observing the frame buffer image. In case that the frame
buffer image is not observed by any handler, the internal
FBO is destroyed. A handler may observe again the frame
buffer image but the FBO has already been destroyed.
This caused an issue with the GaussianBlurView effect which
was using a render task to blur an image and a frabe buffer
image to write the blurred image.
Change-Id: I89a7de6f97ee52fb219f8b7641d4d2bbb42764d5
Signed-off-by: Victor Cebollada <v.cebollada@samsung.com>