Don't call function pointer when it is NULL

(cherry picked from commit dc16a3514096bd53418bccd5c588b53a76d9c676)

src/gpu/d3d12/SDL_gpu_d3d12.c

@@ -9100,17 +9100,14 @@ static SDL_GPUDevice *D3D12_CreateDevice(bool debugMode, bool preferLowPower, SD
     if (SDL_HasProperty(props, SDL_PROP_GPU_DEVICE_CREATE_D3D12_AGILITY_SDK_PATH_STRING) && SDL_HasProperty(props, SDL_PROP_GPU_DEVICE_CREATE_D3D12_AGILITY_SDK_VERSION_NUMBER)) {
         int d3d12SDKVersion = SDL_GetNumberProperty(props, SDL_PROP_GPU_DEVICE_CREATE_D3D12_AGILITY_SDK_VERSION_NUMBER, 0);
         const char *d3d12SDKPath = SDL_GetStringProperty(props, SDL_PROP_GPU_DEVICE_CREATE_D3D12_AGILITY_SDK_PATH_STRING, ".\\D3D12\\");
+        ID3D12SDKConfiguration *sdk_config = NULL;
 
         pD3D12GetInterface = (PFN_D3D12_GET_INTERFACE)SDL_LoadFunction(
             renderer->d3d12_dll,
             D3D12_GET_INTERFACE_FUNC);
         if (pD3D12GetInterface == NULL) {
             SDL_LogWarn(SDL_LOG_CATEGORY_GPU, "Could not load D3D12GetInterface, custom D3D12 SDK will not load.");
-        }
-
-        ID3D12SDKConfiguration *sdk_config = NULL;
-
-        if (SUCCEEDED(pD3D12GetInterface(D3D_GUID(D3D_CLSID_ID3D12SDKConfiguration), D3D_GUID(D3D_IID_ID3D12SDKConfiguration), (void**) &sdk_config))) {
+        } else if (SUCCEEDED(pD3D12GetInterface(D3D_GUID(D3D_CLSID_ID3D12SDKConfiguration), D3D_GUID(D3D_IID_ID3D12SDKConfiguration), (void**) &sdk_config))) {
             ID3D12SDKConfiguration1 *sdk_config1 = NULL;
             if (SUCCEEDED(IUnknown_QueryInterface(sdk_config, &D3D_IID_ID3D12SDKConfiguration1, (void**) &sdk_config1))) {
                 if (SUCCEEDED(ID3D12SDKConfiguration1_CreateDeviceFactory(sdk_config1, d3d12SDKVersion, d3d12SDKPath, &D3D_IID_ID3D12DeviceFactory, (void**) &factory))) {