user update -p without argument allowed

when not giving an argument (to avoid clear passwords in bash history) to "yunohost user update -p", now you are prompted for a password

data/actionsmap/yunohost.yml

@@ -165,8 +165,11 @@ user:
                     full: --change-password
                     help: New password to set
                     metavar: PASSWORD
+                    nargs: "?"
+                    const: 0
                     extra:
                         pattern: *pattern_password
+                        comment: good_practices_about_user_password
                 --add-mailforward:
                     help: Mailforward addresses to add
                     nargs: "*"

src/yunohost/user.py

@@ -325,7 +325,9 @@ def user_update(operation_logger, username, firstname=None, lastname=None, mail=
     if lastname and firstname:
         new_attr_dict['cn'] = new_attr_dict['displayName'] = [firstname + ' ' + lastname]
 
-    if change_password:
+    if change_password is not None:
+        if not change_password:
+            change_password = msignals.prompt(m18n.n("ask_password"), True, True)
         # Ensure sufficiently complex password
         assert_password_is_strong_enough("user", change_password)