Make sure we're actually running on Windows before using D3D renderers

src/render/direct3d/SDL_render_d3d.c

@@ -1598,7 +1598,11 @@ int D3D_CreateRenderer(SDL_Renderer *renderer, SDL_Window *window, Uint32 flags)
     renderer->driverdata = data;
 
     SDL_VERSION(&windowinfo.version);
-    SDL_GetWindowWMInfo(window, &windowinfo);
+    if (!SDL_GetWindowWMInfo(window, &windowinfo) ||
+        windowinfo.subsystem != SDL_SYSWM_WINDOWS) {
+        SDL_free(data);
+        return SDL_SetError("Couldn't get window handle");
+    }
 
     window_flags = SDL_GetWindowFlags(window);
     SDL_GetWindowSizeInPixels(window, &w, &h);

src/render/direct3d11/SDL_render_d3d11.c

@@ -812,7 +812,12 @@ static HRESULT D3D11_CreateSwapChain(SDL_Renderer *renderer, int w, int h)
 #if defined(__WIN32__) || defined(__WINGDK__)
         SDL_SysWMinfo windowinfo;
         SDL_VERSION(&windowinfo.version);
-        SDL_GetWindowWMInfo(renderer->window, &windowinfo);
+        if (!SDL_GetWindowWMInfo(renderer->window, &windowinfo) ||
+            windowinfo.subsystem != SDL_SYSWM_WINDOWS) {
+            SDL_SetError("Couldn't get window handle");
+            result = E_FAIL;
+            goto done;
+        }
 
         result = IDXGIFactory2_CreateSwapChainForHwnd(data->dxgiFactory,
                                                       (IUnknown *)data->d3dDevice,