Elastic: handle pictures without variations or project ID

This happens on old file documents.

pillar/celery/search_index_tasks.py

@@ -41,14 +41,26 @@ def _handle_picture(node: dict, to_index: dict):
     picture = files_collection.find_one(lookup)
 
     img_variation_t = next(
-        (item for item in picture['variations']
+        (item for item in picture.get('variations', [])
          if item['size'] == 't'), None)
 
-    if img_variation_t:
+    if not img_variation_t:
+        return
+
+    try:
+        pic_pid = picture['project']
+    except KeyError:
+        if picture.get('backend') != 'pillar':
+            # We know for sure that locally saved images don't need regeneration,
+            # so don't bother warning about that.
+            log.warning('Picture %s has no project ID, unable to regenerate link',
+                        picture['_id'])
+        to_index['picture'] = img_variation_t['link']
+    else:
         to_index['picture'] = generate_link(
             picture['backend'],
             img_variation_t['file_path'],
-            project_id=str(picture['project']),
+            project_id=str(pic_pid),
             is_public=True)