Fix memory leak & tained value found by static analyzer

Fix memory leak & tained value found by static analyzer

 - Memory leak
  GifMakeMapObject allocate storage for a color map object with the given number of RGB triplet slots.
  So the storage should be freed by calling GifFreeMapObject that is no longer needed.

 - Tained value
  GifWord is type of SWidth, SHeight. It is defined to be integer in Gif.
  So it is not tained to compare GifWord with integer. We add type cast to be clear.

Change-Id: I8c84e0ef05cfefb5f0f995be3bb14c69702a9d8b
Signed-off-by: jiyong.min <jiyong.min@samsung.com>
(cherry picked from commit 0a5832bc0febd743c1334f36117ecebe8448cd6d)