shell32: Add missing parameter check in ISF_Desktop_fnQueryInterface.

dlls/shell32/shfldr_desktop.c

@@ -106,6 +106,8 @@ static HRESULT WINAPI ISF_Desktop_fnQueryInterface(
 
     TRACE ("(%p)->(%s,%p)\n", This, shdebugstr_guid (riid), ppvObj);
 
+    if (!ppvObj) return E_POINTER;
+
     *ppvObj = NULL;
 
     if (IsEqualIID (riid, &IID_IUnknown) ||

dlls/shell32/tests/shfldr_special.c

@@ -224,9 +224,24 @@ if (0)
     CoUninitialize();
 }
 
+static void test_desktop_folder(void)
+{
+    IShellFolder *psf;
+    HRESULT hr;
+
+    hr = SHGetDesktopFolder(&psf);
+    ok(hr == S_OK, "Got %x\n", hr);
+
+    hr = IShellFolder_QueryInterface(psf, &IID_IShellFolder, NULL);
+    ok(hr == E_POINTER, "Got %x\n", hr);
+
+    IShellFolder_Release(psf);
+}
+
 START_TEST(shfldr_special)
 {
     test_parse_for_entire_network();
     test_parse_for_control_panel();
     test_printers_folder();
+    test_desktop_folder();
 }