Reduce API call of FillFrame at gif-loading.

Reduce API call of FillFrame at gif-loading.

If previous frame's rect area is EQUAL with current frame's rect area,
we don't need to call FillFrame.
Because we will iterate that rect area in DecodeImage function.

In that case, Instead of call FillFrame, We just notify DecodeImage
Should fill background as specific color.

It will reduce most of case. Actually, If first frame, we access each pixel
Twice previous. This patch will reduce that access count.

Change-Id: Ica5fe669b6b553dbe55f054da5471dae865595a1
Signed-off-by: Eunki, Hong <eunkiki.hong@samsung.com>