[books] Fix no result for detail lookup

vrobbler/apps/books/sources/semantic.py

@@ -38,6 +38,9 @@ def lookup_paper_from_semantic(title: str) -> dict:
 
     result = json.loads(response.content)
 
+    if not result:
+        return paper_dict
+
     page_str = result.get("journal", {}).get("pages")
     if page_str:
         try: