fix segfault when invoked with -h

mm/mm.c

@@ -7,6 +7,7 @@
 #if !defined EX_OK || !defined EX_USAGE
 #	include <sysexits.h>
 #endif
+extern int errno;
 
 struct Io_ex{
 	size_t s;
@@ -49,6 +50,9 @@ static struct Io *
 Io_destruct(struct Io *io){
 	size_t i;
 
+	if(io->s == -1)
+		io->s = 0;
+
 	for(i = 0; i < io->s; ++i)
 		fclose(io->files[i]);