[FIX] web: emptylist helper position

Before this commit:

An empty list helper position not centered when search panel sidebar is
there and some issue created while having a droplet on it as the
position will shifting after a few seconds (sign_tour)

After this commit:

Set an empty list helper at a relative position and now it will always be
displayed at the center whenever have a search panel sidebar

LINKS

Task-2323988

closes odoo/odoo#56792

X-original-commit: d50c7f5c88eaef56c757849a64d63f92bd73f2f2
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>

addons/web/static/src/scss/search_panel.scss

@@ -15,6 +15,7 @@ $o-searchpanel-filter-default-color: #D59244;
         flex: 1 1 100%;
         overflow: auto; // make the renderer and search panel scroll individually
         max-height: 100%;
+        position: relative;
     }
 }