Use SDL_AllocFormat instead of creating it manually

According to the docs, `SDL_PixelFormat` is a read-only structure.
Creating it manually leaves out some important fields like `format` and
`next` pointer to be undefined.

Signed-off-by: Marcin Serwin <marcin@serwin.dev>

Author: marcin-serwin

src_c/surface.c

@@ -4540,29 +4540,13 @@ pgSurface_Blit(pgSurfaceObject *dstobj, pgSurfaceObject *srcobj,
         }
         else {
             SDL_PixelFormat *fmt = src->format;
-            SDL_PixelFormat newfmt;
+            SDL_PixelFormat *newfmt =
+                SDL_AllocFormat(SDL_MasksToPixelFormatEnum(
+                    fmt->BitsPerPixel, fmt->Rmask, fmt->Gmask, fmt->Bmask, 0));
 
-            newfmt.palette = 0; /* Set NULL (or SDL gets confused) */
-#if SDL_VERSION_ATLEAST(3, 0, 0)
-            newfmt.bits_per_pixel = fmt->bits_per_pixel;
-            newfmt.bytes_per_pixel = fmt->bytes_per_pixel;
-#else
-            newfmt.BitsPerPixel = fmt->BitsPerPixel;
-            newfmt.BytesPerPixel = fmt->BytesPerPixel;
-#endif
-            newfmt.Amask = 0;
-            newfmt.Rmask = fmt->Rmask;
-            newfmt.Gmask = fmt->Gmask;
-            newfmt.Bmask = fmt->Bmask;
-            newfmt.Ashift = 0;
-            newfmt.Rshift = fmt->Rshift;
-            newfmt.Gshift = fmt->Gshift;
-            newfmt.Bshift = fmt->Bshift;
-            newfmt.Aloss = 0;
-            newfmt.Rloss = fmt->Rloss;
-            newfmt.Gloss = fmt->Gloss;
-            newfmt.Bloss = fmt->Bloss;
-            src = PG_ConvertSurface(src, &newfmt);
+            src = PG_ConvertSurface(src, newfmt);
+
+            SDL_FreeFormat(newfmt);
             if (src) {
 #if SDL_VERSION_ATLEAST(3, 0, 0)
                 result = SDL_BlitSurface(src, srcrect, dst, dstrect) ? 0 : -1;