...

src/calibre/srv/content.py

@@ -245,6 +245,7 @@ def get(ctx, rd, what, book_id, library_id):
             sz = rd.query.get('sz')
             w, h = 60, 80
             if sz is None:
+                if rest:
                     try:
                         w, h = map(int, rest.split('_'))
                     except Exception: