[clip] Script fails when encountering an unknown message type

[boxanm]

When processing a rosbag containing an unknown message type, the clip tool ends raising a rosbags.typesys.base.TypesysError.
A preferred behavior, in my opinion, would be to notify the user about it but process the rest of the bag file.

[RedLeader962]

Same here

$ rosbag-tools topic-remove -f -t /diagnostics rosbag2_2023_09_25-14_20_35

/usr/local/lib/python3.8/dist-packages/rosbag_tools/topic_remove/topic_remover.py:164: UserWarning: Output path rosbag2_2023_09_25-14_20_35_filt already exists, output overwriting flag has been set, deleting old output file
  warnings.warn(
Traceback (most recent call last):
  File "/usr/local/bin/rosbag-tools", line 8, in <module>
    sys.exit(cli_main())
  File "/usr/local/lib/python3.8/dist-packages/click/core.py", line 1157, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/lib/python3.8/dist-packages/click/core.py", line 1078, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib/python3.8/dist-packages/click/core.py", line 1688, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.8/dist-packages/click/core.py", line 1434, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python3.8/dist-packages/click/core.py", line 783, in invoke
    return __callback(*args, **kwargs)
  File "/usr/local/lib/python3.8/dist-packages/rosbag_tools/utils.py", line 75, in wrapper
    return f(*args, **kwargs)
  File "/usr/local/lib/python3.8/dist-packages/rosbag_tools/topic_remove/main.py", line 59, in cli
    rosbag_rem.export(default_outpath, force_output_overwrite=force)
  File "/usr/local/lib/python3.8/dist-packages/rosbag_tools/topic_remove/topic_remover.py", line 196, in export
    conn_map[conn.id] = writer.add_connection(
  File "/usr/local/lib/python3.8/dist-packages/rosbags/rosbag2/writer.py", line 195, in add_connection
    msgdef, _ = generate_msgdef(msgtype, ros_version=2)
  File "/usr/local/lib/python3.8/dist-packages/rosbags/typesys/msg.py", line 493, in generate_msgdef
    msgdef, md5sum = gendefhash(typename, subdefs, typestore, ros_version)
  File "/usr/local/lib/python3.8/dist-packages/rosbags/typesys/msg.py", line 405, in gendefhash
    raise TypesysError(f'Type {typename!r} is unknown.')
rosbags.typesys.base.TypesysError: Type 'rosbridge_msgs/msg/ConnectedClients' is unknown.

I figure we need to use the --msg-path <path/to/custom/msg> flag in that case. If that so, maybe the script could handle the error and tell the user about proper usage recommandation