SDL: Use DefWindowProc for the initial SDL window proc

SDL Commits
1 
From 6c4f2bd83d1942ee98c7424a0b627ca518c98feb Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Sun, 2 Nov 2025 07:18:49 -0800
Subject: [PATCH] Use DefWindowProc for the initial SDL window proc

This makes sure that anything that hooks window creation to set up window proc hooks will call DefWindowProc instead of infinitely recursing when we set up our window proc afterwards.

Fixes https://github.com/libsdl-org/SDL/issues/10529
---
 src/video/windows/SDL_windowsevents.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/src/video/windows/SDL_windowsevents.c b/src/video/windows/SDL_windowsevents.c
index 9854767c3054e..5bbcbf7b1dce8 100644
--- a/src/video/windows/SDL_windowsevents.c
+++ b/src/video/windows/SDL_windowsevents.c
@@ -2729,18 +2729,12 @@ bool SDL_RegisterApp(const char *name, Uint32 style, void *hInst)
     SDL_Instance = hInst ? (HINSTANCE)hInst : GetModuleHandle(NULL);
 
     // Register the application class
+    SDL_zero(wcex);
     wcex.cbSize = sizeof(WNDCLASSEX);
-    wcex.hCursor = NULL;
-    wcex.hIcon = NULL;
-    wcex.hIconSm = NULL;
-    wcex.lpszMenuName = NULL;
     wcex.lpszClassName = SDL_Appname;
     wcex.style = SDL_Appstyle;
-    wcex.hbrBackground = NULL;
-    wcex.lpfnWndProc = WIN_WindowProc;
+    wcex.lpfnWndProc = DefWindowProc;
     wcex.hInstance = SDL_Instance;
-    wcex.cbClsExtra = 0;
-    wcex.cbWndExtra = 0;
 
 #if !defined(SDL_PLATFORM_XBOXONE) && !defined(SDL_PLATFORM_XBOXSERIES)
     hint = SDL_GetHint(SDL_HINT_WINDOWS_INTRESOURCE_ICON);