Fix for the fix cover_url

cps/editbooks.py

@@ -613,14 +613,15 @@ def edit_book(book_id):
 
         if not error:
             if "cover_url" in to_save:
-                if not current_user.role_upload() and to_save["cover_url"] != "":
-                    return "", (403)
-                result, error = helper.save_cover_from_url(to_save["cover_url"], book.path)
-                if result is True:
-                    book.has_cover = 1
-                    modif_date = True
-                else:
-                    flash(error, category="error")
+                if to_save["cover_url"]:
+                    if not current_user.role_upload():
+                        return "", (403)
+                    result, error = helper.save_cover_from_url(to_save["cover_url"], book.path)
+                    if result is True:
+                        book.has_cover = 1
+                        modif_date = True
+                    else:
+                        flash(error, category="error")
 
             # Add default series_index to book
             modif_date |= edit_book_series_index(to_save["series_index"], book)