perf header: Fix divide by zero error if f_header.attr_size==0

So I have been having lots of trouble with hand-crafted perf.data files
causing segfaults and the like, so I have started fuzzing the perf tool.

First issue found:

If f_header.attr_size is 0 in the perf.data file, then perf will crash
with a divide-by-zero error.

Committer note:

Added a pr_err() to tell the user why the command failed.

Signed-off-by: Vince Weaver <vincent.weaver@maine.edu>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.21.1907231100440.14532@macbook-air
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>