sdl12-compat: Don't add the 2.0->1.2 event conversion filter twice

SDL Commits
1 
From 1cc3061c06877a7ee4277187aa59dcca755e5a7f Mon Sep 17 00:00:00 2001
From: David Gow <[EMAIL REDACTED]>
Date: Thu, 15 Jul 2021 18:16:35 +0800
Subject: [PATCH] Don't add the 2.0->1.2 event conversion filter twice

If the program creates several windows (such as Unreal Tournament 2004's
splash screen), the Event Filter used to convert SDL 2.0 events to SDL
1.2 events can end up being added twice, which causes events to be
converted twice).

Unconditionally remove the event filter in Init12Video() before
adding it, to ensure it only ever appears once. This fixes issue #119.
---
 src/SDL12_compat.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/SDL12_compat.c b/src/SDL12_compat.c
index 67fb133..d7ff76b 100644
--- a/src/SDL12_compat.c
+++ b/src/SDL12_compat.c
@@ -1734,6 +1734,7 @@ Init12Video(void)
     SupportSysWM = SDL_FALSE;
 #endif
 
+    SDL20_DelEventWatch(EventFilter20to12, NULL);
     SDL20_AddEventWatch(EventFilter20to12, NULL);
 
     VideoDisplayIndex = GetVideoDisplay();