user32: Call DefWindowProc() in DesktopWndProc().

This fixes a regression introduced by commit
fc14753dc0.

WM_NCCALCSIZE is not handled yet because it initiates loading the
driver again.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=45485
Signed-off-by: Józef Kucia <jkucia@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>

dlls/user32/desktop.c

@@ -127,8 +127,10 @@ LRESULT WINAPI DesktopWndProc( HWND hwnd, UINT message, WPARAM wParam, LPARAM lP
         }
         return TRUE;
     }
+    case WM_NCCALCSIZE:
+        return 0;
     default:
-        return 0;  /* all other messages are ignored */
+        return DefWindowProcW( hwnd, message, wParam, lParam );
     }
 }