msxml3/tests: Initialize string pointer on default case too (Coverity).

Signed-off-by: Nikolay Sivov <nsivov@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>

dlls/msxml3/tests/domdoc.c

@@ -12086,6 +12086,7 @@ static void test_put_data(void)
               break;
            }
            default:
+              get_data = NULL;
               break;
        }