shared/image: Silence maybe-uninitialized warning

shared/image-loader.c: In function 'load_image':
shared/image-loader.c:434:12: warning: 'image' may be used uninitialized
in this function [-Wmaybe-uninitialized]
  } else if (!image) {
              ^

Warning produced by GCC 5.3 and 6.1, with -Og.

Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>
Reviewed-by: Giulio Camuffo <giuliocamuffo@gmail.com>

shared/image-loader.c

@@ -396,7 +396,7 @@ static const struct image_loader loaders[] = {
 pixman_image_t *
 load_image(const char *filename)
 {
-	pixman_image_t *image;
+	pixman_image_t *image = NULL;
 	unsigned char header[4];
 	FILE *fp;
 	unsigned int i;
@@ -431,7 +431,6 @@ load_image(const char *filename)
 		fprintf(stderr, "%s: unrecognized file header "
 			"0x%02x 0x%02x 0x%02x 0x%02x\n",
 			filename, header[0], header[1], header[2], header[3]);
-		image = NULL;
 	} else if (!image) {
 		/* load probably printed something, but just in case */
 		fprintf(stderr, "%s: error reading image\n", filename);