sdl12-compat: Fixed crash if SDL_WM_SetIcon() is passed a NULL icon

SDL Commits
1 
From 7df3288587905a224635001ff285a8d621cccb90 Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Mon, 12 Sep 2022 20:52:15 -0700
Subject: [PATCH] Fixed crash if SDL_WM_SetIcon() is passed a NULL icon

---
 src/SDL12_compat.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/SDL12_compat.c b/src/SDL12_compat.c
index 3bb9445e..ba3112ef 100644
--- a/src/SDL12_compat.c
+++ b/src/SDL12_compat.c
@@ -6693,6 +6693,11 @@ SDL_WM_SetIcon(SDL12_Surface *icon12, Uint8 *mask)
     int bpp;
     int ret;
 
+    /* Make sure we actually have an icon to set */
+    if (!icon12) {
+        return;
+    }
+
     /* take the mask and zero out those alpha values. */
     oldmode = SDL_BLENDMODE_NONE;
     if (SDL20_GetSurfaceBlendMode(icon12->surface20, &oldmode) < 0) {