Fix a regression in previous release that broke copying of book to an…

…other library if the books author does not exist in the destination database.

src/calibre/db/tables.py

@@ -286,7 +286,7 @@ def item_ids_for_names(self, db, item_names: Iterable[str], case_sensitive: bool
             for iid, name in self.id_map.items():
                 if icu_lower(name) == q:
                     return {item_names[0]: iid}
-            return {item_names[0]: iid}
+            return {item_names[0]: None}
         rmap = {icu_lower(v) if isinstance(v, str) else v:k for k, v in self.id_map.items()}
         return {name: rmap.get(icu_lower(name) if isinstance(name, str) else name, None) for name in item_names}