Specify text encoding for zero-fill map file

scripts/wk/clone/ddrescue.py

@@ -2242,7 +2242,7 @@ def zero_fill_destination(state: State, dry_run: bool = True) -> None:
       )
     io.copy_file(block_pair.map_path, zero_map_path, overwrite=True)
     if larger_destination:
-      with open(zero_map_path, 'a') as f:
+      with open(zero_map_path, 'a', encoding='utf-8') as f:
         f.write(
           f'{hex(block_pair.size)}  '
           f'{hex(destination_size - block_pair.size)}  ?'