contrib: sdl_image: disable package not usable on Winstore builds

depends on sdl which is not usable

contrib/src/SDL_image/rules.mak

@@ -3,7 +3,9 @@
 SDL_IMAGE_VERSION := 1.2.12
 SDL_IMAGE_URL := http://www.libsdl.org/projects/SDL_image/release/SDL_image-$(SDL_IMAGE_VERSION).tar.gz
 
+ifndef HAVE_WINSTORE
 PKGS += SDL_image
+endif
 ifeq ($(call need_pkg,"SDL_image"),)
 PKGS_FOUND += SDL_image
 endif
@@ -20,10 +22,8 @@ SDL_image: SDL_image-$(SDL_IMAGE_VERSION).tar.gz .sum-SDL_image
 	$(UPDATE_AUTOCONFIG)
 	$(MOVE)
 
-DEPS_SDL_image = jpeg $(DEPS_jpeg) tiff $(DEPS_tiff)
-ifndef HAVE_WINSTORE
-DEPS_SDL_image += sdl $(DEPS_sdl)
-endif
+DEPS_SDL_image = jpeg $(DEPS_jpeg) tiff $(DEPS_tiff) \
+	sdl $(DEPS_sdl)
 
 .SDL_image: SDL_image
 	cd $< && $(HOSTVARS) ./configure $(HOSTCONF) --enable-tif --disable-sdltest --disable-png