cmdline client: Improve error message when passing an empty TraceConfig am: 21bf7f8144
cmdline client: Improve error message when passing an empty TraceConfig
am: 21bf7f8144

Change-Id: I78a379466379aa05e38719317a42221580a42775

google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto