Before this fix, ffmpeg -h full | grep map get the command dump
like:

-map [-]input_file_id[:stream_specifier][,sync_file_id[:stream_s  set input stream mapping
                                                               ^
                                                               |
							    truncated
after this fix, we can get full option dump.
Found-by: vacingfang <vacingfang@tencent.com>
Signed-off-by: Jun Zhao <barryjzhao@tencent.com>