Do not disable send password by Talk without setting new password in UI

Before it was possible to disable "send password by Talk" without
setting a new password, so the UI allowed that. Now that the server
prevents it the UI had to be adjusted to not update the share until a
new password is set when "send password by Talk" is disabled.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>