perf machine: Null-terminate version char array upon fgets(/proc/version) error

If fgets() fails due to any other error besides end-of-file, the version
char array may not even be null-terminated.

Signed-off-by: Donald Yandt <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Avi Kivity <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Yanmin Zhang <[e-mail]>
Fixes: a1645ce12adb ("perf: 'perf kvm' tool for monitoring guest performance from host")
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/machine.c

···
 	if (!file)
 		return NULL;
 
-	version[0] = '\0';
 	tmp = fgets(version, sizeof(version), file);
+	if (!tmp)
+		*version = '\0';
 	fclose(file);
 
 	name = strstr(version, prefix);