use NSIG for signal table

Index: main.c
--- main.c.orig
+++ main.c
@@ -174,7 +174,7 @@ sanitize_signals(void)
     struct sigaction dfl = {.sa_handler = SIG_DFL};
     sigemptyset(&dfl.sa_mask);
 
-    for (int i = 1; i < SIGRTMAX; i++)
+    for (int i = 1; i < NSIG; i++)
         sigaction(i, &dfl, NULL);
 }
 
