[FIX] website: slide position gallery snippet

Changing position of a slide from the gallery snippet was not working.

saas-6 part of #9284
opw-653061
opw-653167

addons/website/static/src/js/website.snippets.gallery.js

@@ -220,7 +220,7 @@
             var $container = this.$target.find(".container:first");
             var editor = new website.editor.MediaDialog(this.$target.closest('.o_editable'), null, {select_images: true});
             editor.appendTo(document.body);
-            var index = Math.max(_.map(this.$target.find("img").get(), function (img) { return img.dataset.index | 0; })) + 1;
+            var index = Math.max(0, _.max(_.map(this.$target.find("img").get(), function (img) { return img.dataset.index | 0; })) + 1);
             editor.on('saved', this, function (attachments) {
                 for (var i = 0 ; i < attachments.length; i++) {
                     var img = $('<img class="img img-responsive mb8 mt8"/>')
@@ -327,7 +327,6 @@
             if (type !== "click") return;
 
             var $parent = this.$target.closest("section");
-            this.BuildingBlock.create_overlay($parent);
             var editor = $parent.data('snippet-editor').styles.gallery;
             var imgs = $parent.find('img').get();
             imgs.sort(function (a,b) { return $(a).data('index')-$(b).data('index'); });