plugin chat: fixed dropdown: dropdown was calling "open" each time a key was pressed, abd open is calling dismiss if dropdown is already opened. But dismiss is calling _real_dissmiss with a schedule, resulting in incoherent state and the dropdown not closed when expected. A check is now done to call "open" only when there is not already a dropdown, and to call dismiss when the text input is empty.

-e git+https://github.com/kivy/kivy.git#egg=kivy
-e hg+https://repos.goffi.org/sat#egg=sat
-e .