Fixed bug 5037 - Regression 2.0.12 Alpha value of 0 on palette may become opaque

(see also bug 3827)

src/render/SDL_render.c

@@ -1165,12 +1165,10 @@ SDL_CreateTextureFromSurface(SDL_Renderer * renderer, SDL_Surface * surface)
 
     /* If Palette contains alpha values, promotes to alpha format */
     if (fmt->palette) {
-        for (i = 0; i < fmt->palette->ncolors; i++) {
-            Uint8 alpha_value = fmt->palette->colors[i].a;
-            if (alpha_value != 0 && alpha_value != SDL_ALPHA_OPAQUE) {
-                needAlpha = SDL_TRUE;
-                break;
-            }
+        SDL_bool is_opaque, has_alpha_channel;
+        SDL_DetectPalette(fmt->palette, &is_opaque, &has_alpha_channel);
+        if (!is_opaque) {
+            needAlpha = SDL_TRUE;
         }
     }