SDL: Fix rounding in MULT_DIV_255

From 5d875aa94e2e19a138079156218b3d46c015f6d7 Mon Sep 17 00:00:00 2001
From: Brick <[EMAIL REDACTED]>
Date: Wed, 3 Jul 2024 14:36:50 +0100
Subject: [PATCH] Fix rounding in MULT_DIV_255

---
 src/video/SDL_blit.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/video/SDL_blit.h b/src/video/SDL_blit.h
index a59c9a603c3e5..b994f9e9bd592 100644
--- a/src/video/SDL_blit.h
+++ b/src/video/SDL_blit.h
@@ -513,6 +513,7 @@ extern SDL_BlitFunc SDL_CalculateBlitA(SDL_Surface *surface);
 #define MULT_DIV_255(sC, dC, out) \
     do {                          \
         Uint16 x = sC * dC;       \
+        x += 0x1U;                \
         x += x >> 8;              \
         out = x >> 8;             \
     } while (0)