When we don't know existing files count, we assume that there are existing files

Co-authored-by: Fokko Driesprong <[email protected]>

Author: zhjwpku

src/iceberg/manifest_list.h

@@ -163,7 +163,7 @@ struct ICEBERG_EXPORT ManifestFile {
   bool has_added_files() const { return added_files_count.value_or(1) > 0; }
 
   /// \brief Checks if this manifest file contains entries with EXISTING status.
-  bool has_existing_files() const { return existing_files_count.value_or(-1) > 0; }
+  bool has_existing_files() const { return existing_files_count.value_or(1) > 0; }
 
   /// \brief Checks if this manifest file contains entries with DELETED status
   bool has_deleted_files() const { return deleted_files_count.value_or(-1) > 0; }