perf inject: Fix output from a pipe to a file

Sometimes it needs to save the perf inject data to a file for debugging.
But normally it assumes the same format for input and output, so the end
result cannot be used due to a broken format.

  # perf record -a -o - sleep 1 | perf inject -b -o my.data

  # perf report -i my.data --stdio
  0x208 [0]: failed to process type: 0 [Invalid argument]
  Error:
  failed to process sample
  # To display the perf.data header info, please use --header/--header-only options.
  #

In this case, it thought the data has a regular file header since the
output is not a pipe.  But actually it doesn't have one and has a pipe
file header.  At the end of the session, it tries to rewrite the regular
file header with updated features and it overwrites the data just
follows the pipe header.

Fix it by checking either the input and the output is a pipe.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20210719223153.1618812-4-namhyung@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>