Namhyung reported segfault in perf daemon start command.

It's caused by extra check on argv[0] which is set to NULL by previous
__cmd_start call. Adding missing else to skip the extra check.

Fixes: 92294b90 ("perf daemon: Dynamically allocate path to perf")
Reported-and-Tested-by: Namhyung Kim <namhyung@kernel.org>
Reported-by: Thomas Richter <tmricht@linux.ibm.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Link: https://lore.kernel.org/r/20230626201606.2514679-1-jolsa@kernel.orgSigned-off-by: Namhyung Kim <namhyung@kernel.org>