[FIX] website: use relative url in background image

Use .css convert into absolute url

addons/website/static/src/js/website.editor.js

@@ -1863,6 +1863,9 @@ define(['summernote/summernote'], function () {
             $(document.body).trigger("media-saved", [self.active.media, self.old_media]);
             self.trigger("saved", [self.active.media, self.old_media]);
             setTimeout(function () {
+                if (!self.active.media.parentNode) {
+                    return;
+                }
                 range.createFromNode(self.active.media).select();
                 click_event(self.active.media, "mousedown");
                 if (!this.only_images) {

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

@@ -1059,7 +1059,7 @@
         },
         background: function(type, value, $li) {
             if (value && value.length) {
-                this.$bg.css("background-image", 'url(' + value + ')');
+                this.$bg.attr("style", 'background-image: url(' + value + ')' + this.$bg.attr("style").replace(/background-image:[^;]+/, '') );
                 this.$bg.addClass("oe_img_bg");
             } else {
                 this.$bg.css("background-image", "");