SDL: `SDL_RenderSetVSync()`: Restrict `vsync` to 0 or 1

SDL Commits
1 
From 4a9947336ca0126f03e04114f568674a6bdb727b Mon Sep 17 00:00:00 2001
From: Misa <[EMAIL REDACTED]>
Date: Tue, 14 Sep 2021 15:51:17 -0700
Subject: [PATCH] `SDL_RenderSetVSync()`: Restrict `vsync` to 0 or 1

In the future, we might want to support special swap intervals. To
prevent applications from expecting nonzero values of vsync to be the
same as "on", fail with SDL_Unsupported() if the value passed is neither
0 nor 1.
---
 include/SDL_render.h    | 2 +-
 src/render/SDL_render.c | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/SDL_render.h b/include/SDL_render.h
index f8e5e6ca96..c576196574 100644
--- a/include/SDL_render.h
+++ b/include/SDL_render.h
@@ -1698,7 +1698,7 @@ extern DECLSPEC void *SDLCALL SDL_RenderGetMetalCommandEncoder(SDL_Renderer * re
  * Toggle VSync of the given renderer.
  *
  * \param renderer The renderer to toggle
- * \param vsync Non-zero for on, zero for off
+ * \param vsync 1 for on, 0 for off. All other values are reserved
  * \returns a 0 int on success, or non-zero on failure
  */
 extern DECLSPEC int SDLCALL SDL_RenderSetVSync(SDL_Renderer* renderer, int vsync);
diff --git a/src/render/SDL_render.c b/src/render/SDL_render.c
index eec6dc9bb7..b0b3ad700f 100644
--- a/src/render/SDL_render.c
+++ b/src/render/SDL_render.c
@@ -4129,6 +4129,10 @@ SDL_RenderSetVSync(SDL_Renderer * renderer, int vsync)
 {
     CHECK_RENDERER_MAGIC(renderer, -1);
 
+    if (vsync != 0 && vsync != 1) {
+        return SDL_Unsupported();
+    }
+
     if (renderer->SetVSync) {
         return renderer->SetVSync(renderer, vsync);
     }