SDL_image: IMG_gif.c (ReadImage): return NULL if ImageNewCmap() returns NULL.

SDL Commits
1 
From 6f6dd3c4ad2d46936d014b977a274071b5cfa5ae Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Tue, 20 Jul 2021 17:51:10 +0300
Subject: [PATCH] IMG_gif.c (ReadImage): return NULL if ImageNewCmap() returns
 NULL.

Fixes: https://github.com/libsdl-org/SDL_image/issues/180
---
 IMG_gif.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/IMG_gif.c b/IMG_gif.c
index 8e20f41..b00e7c1 100644
--- a/IMG_gif.c
+++ b/IMG_gif.c
@@ -642,6 +642,9 @@ ReadImage(SDL_RWops * src, int len, int height, int cmapSize,
         return NULL;
     }
     image = ImageNewCmap(len, height, cmapSize);
+    if (!image) {
+        return NULL;
+    }
 
     for (i = 0; i < cmapSize; i++)
         ImageSetCmap(image, i, cmap[CM_RED][i],