HLS: Fix map data exists check when merging segments

`map_data` may resolve Truthy, while `map_data[1]` itself could be None, resulting in `None` being written to the stream.

devine/core/manifests/hls.py

@@ -306,7 +306,7 @@ def merge(to: Path, via: list[Path], delete: bool = False, include_map_data: boo
                     include_map_data: Whether to include the init map data.
                 """
                 with open(to, "wb") as x:
-                    if include_map_data and map_data:
+                    if include_map_data and map_data and map_data[1]:
                         x.write(map_data[1])
                     for file in via:
                         x.write(file.read_bytes())