Add record image not to listing entry

[fisch42]

When showListings is enabled, the listing got the image from the record from which the listing was generated.

This code is preventing this behaviour. No image is added to the listing entry in the sitemap.

[xiaohutai]

Thanks!

[xiaohutai]

There's a small mistake on:

-        {%- if record|link is not empty -%}
+        {%- if if not isListing and record|link is not empty -%}

and I moved this code to the image check so it works as intended in #14.