SDL: Update METAL backend: fix a typo in drawline

SDL Commits
#1 
From 5828cc415a0e4bde9dd27f57dd963925a84c3b4e Mon Sep 17 00:00:00 2001
From: Sylvain <[EMAIL REDACTED]>
Date: Tue, 16 Mar 2021 21:54:27 +0100
Subject: [PATCH] Update METAL backend: fix a typo in drawline

---
 src/render/metal/SDL_render_metal.m | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/render/metal/SDL_render_metal.m b/src/render/metal/SDL_render_metal.m
index 6de16849b8..dc61997aed 100644
--- a/src/render/metal/SDL_render_metal.m
+++ b/src/render/metal/SDL_render_metal.m
@@ -1142,7 +1142,7 @@ - (void)dealloc
        angles. Maybe !!! FIXME for later, though. */
 
     points -= 2;  /* update the last line. */
-    verts -= (count * 2) - 2;
+    verts -= 2 + 4;
 
     const float xstart = points[0].x;
     const float ystart = points[0].y;