SDL: Fixed bug #2881 - SDL_RLEsurface may encode RGB888 if it has no color key (Thanks Simon Hug)

From c93e3b36074ddb2ed986cbacc5e9d4f3a60db343 Mon Sep 17 00:00:00 2001
From: Sylvain <[EMAIL REDACTED]>
Date: Wed, 28 Apr 2021 10:43:28 +0200
Subject: [PATCH] Fixed bug #2881 - SDL_RLEsurface may encode RGB888 if it has
 no color key (Thanks Simon Hug) To encode with BLEND mode, it needs a valid
 alpha channel

---
 src/video/SDL_RLEaccel.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/video/SDL_RLEaccel.c b/src/video/SDL_RLEaccel.c
index 32cf8e074..3f3b62cec 100644
--- a/src/video/SDL_RLEaccel.c
+++ b/src/video/SDL_RLEaccel.c
@@ -1423,9 +1423,12 @@ SDL_RLESurface(SDL_Surface * surface)
         return -1;
     }
 
-    /* If we don't have colorkey or blending, nothing to do... */
-    flags = surface->map->info.flags;
-    if (!(flags & (SDL_COPY_COLORKEY | SDL_COPY_BLEND))) {
+    if (flags & SDL_COPY_COLORKEY) {
+        /* ok */
+    } else if ((flags & SDL_COPY_BLEND) && surface->format->Amask) {
+        /* ok */
+    } else {
+        /* If we don't have colorkey or blending, nothing to do... */
         return -1;
     }