shell32/autocomplete: Reset the enumerator when the text is empty even when auto-suggest is disabled.

This is needed for auto-append only AutoComplete controls.
Signed-off-by: Gabriel Ivăncescu <gabrielopcode@gmail.com>
Signed-off-by: Huw Davies <huw@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>