add pledge(2) to "mutool draw"

Index: source/tools/mudraw.c
--- source/tools/mudraw.c.orig
+++ source/tools/mudraw.c
@@ -34,6 +34,8 @@
 #include "mupdf/helpers/mu-threads.h"
 #endif
 
+#include <errno.h>
+#include <unistd.h>
 #include <string.h>
 #include <limits.h>
 #include <stdlib.h>
@@ -2145,6 +2147,12 @@ int mudraw_main(int argc, char **argv)
 
 	if (fz_optind == argc)
 		return usage();
+
+	if (pledge("stdio rpath wpath cpath", NULL) == -1)
+	{
+		fprintf(stderr, "pledge: %s\n", strerror(errno));
+		exit(1);
+	}
 
 	if (num_workers > 0)
 	{