Fix Rasterize not works when SetTransform is first time

Fix Rasterize not works when SetTransform is first time

It is possible that SVG load complete, and after than layout executed.

If then, mDefaultSize of SVG is not zero, and rasterize task not requested.

Unfortunatly, if fitting mode settup into image view, the required size
of resterize might not correct. So, ImageView try to re-layout once again
at it's OnResourceReady signal.

This patch make we send rasterize signal at least one time, So let we ensure
the ImageView resource ready signal comes at least one time.

Change-Id: I3edb6a1a681898b007ef1b70470993da5c68c289
Signed-off-by: Eunki, Hong <eunkiki.hong@samsung.com>