perf_counter: tool: handle 0-length data files

Avoid perf-report barfing on 0-length data files.

[ Impact: fix perf-report SIGBUS ]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <20090501102533.196245693@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

Documentation/perf_counter/perf-report.cc

@@ -402,6 +402,11 @@ int main(int argc, char *argv[])
 		exit(-1);
 	}
 
+	if (!stat.st_size) {
+		fprintf(stderr, "zero-sized file, nothing to do!\n");
+		exit(0);
+	}
+
 	load_kallsyms();
 
 remap: