make it possible to compute producer from form dict (#22543)

combo_plugin_gnm/templatetags/gnm.py

@@ -336,6 +336,15 @@ PRODUCER_LABELS = {
 
 @register.filter
 def as_producer(slug):
+    if isinstance(slug, dict):
+        # actually a form
+        for keyword in slug.get('keywords') or []:
+            if keyword.startswith('producer-'):
+                slug = keyword.split('-', 1)[1]
+                break
+        else:
+            slug = slug.get('site_slug')
+
     producer = None
     if ':' in slug: # formdef_reference
         slug = slug.split(':')[0]