correct link to compound image in schema.org data

ippisite/ippidb/templates/compound_card.html

@@ -579,7 +579,7 @@
 {% endif %}
 "@type": "MolecularEntity",
 {% if compound.chembl_id %}
-"image": "https://www.ebi.ac.uk/chembl/api/data/image/{{chembl_id}}.svg",
+"image": "https://www.ebi.ac.uk/chembl/api/data/image/{{ compound.chembl_id }}.svg",
 {% endif %}
 {% if compound.canonical_smile %}
 "smiles": [