Use a promise based API for Record.pre_validate()

Closes #12039
(grafted from 2e62e2dc88702ffdcb98ac3185b92e08ae2af937)

--HG--
branch : 6.0

sao/src/model.js

@@ -1302,12 +1302,7 @@
             var values = this._get_on_change_args(
                 Object.keys(this._changed).concat(['id']));
             return this.model.execute('pre_validate',
-                    [values], this.get_context())
-                .then(function() {
-                    return true;
-                }, function() {
-                    return false;
-                });
+                    [values], this.get_context());
         },
         cancel: function() {
             this._loaded = {};

sao/src/window.js

@@ -430,7 +430,10 @@
                     this.screen.current_record) {
                 this.screen.current_record.validate().then(function(validate) {
                     if (validate && this.screen.attributes.pre_validate) {
-                        return this.screen.current_record.pre_validate();
+                        return this.screen.current_record.pre_validate().then(
+                            function () { return true; },
+                            function () { return false; }
+                        );
                     }
                     return validate;
                 }.bind(this)).then(function(validate) {