Use a promise based API for Record.pre_validate()

Closes #12039

sao/src/model.js

@@ -1262,8 +1262,7 @@
             var values = this._get_on_change_args(
                 Object.keys(this.modified_fields).concat(['id']));
             return this.model.execute('pre_validate',
-                    [values], this.get_context())
-                .then(() => true, () => false);
+                    [values], this.get_context());
         },
         cancel: function() {
             this._loaded = {};

sao/src/window.js

@@ -479,7 +479,10 @@
                     this.screen.current_record) {
                 this.screen.current_record.validate().then(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;
                 }).then(validate => {