Contribs: update SDLimage to 1.2.12

(cherry picked from commit eb7207e8)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

contrib/src/SDL_image/SHA512SUMS

-0ccdde079d62979f5e482711eca40db65dbf791ceb36ff6c9bc5ac43b5187f61403876f1c4a8628cdc932e4b07ed09ae7ab6c1e05d998fa4e80c5efbd7a5ed0b  SDL_image-1.2.10.tar.gz
+0e71b280abc2a7f15755e4480a3c1b52d41f9f8b0c9216a6f5bd9fc0e939456fb5d6c10419e1d1904785783f9a1891ead278c03e88b0466fecc6871c3ca40136  SDL_image-1.2.12.tar.gz

contrib/src/SDL_image/rules.mak

 # SDL_image
 
-SDL_IMAGE_VERSION := 1.2.10
+SDL_IMAGE_VERSION := 1.2.12
 SDL_IMAGE_URL := http://www.libsdl.org/projects/SDL_image/release/SDL_image-$(SDL_IMAGE_VERSION).tar.gz
 
 PKGS += SDL_image