open() takes three arguments when used with O_CREAT.
Furthermore, opening "/dev/null" and unsuccessfully creating it if it does
not exist and assuming everything's ok in that case makes no sense either.
Fix the test to be a bit more sane.

Lubomir Rintel <lkundrak@v3.sk>

diff -up cpm-0.23beta/security.c.open cpm-0.23beta/security.c
--- cpm-0.23beta/security.c.open	2009-01-08 16:45:49.000000000 +0100
+++ cpm-0.23beta/security.c	2009-01-08 16:46:54.000000000 +0100
@@ -495,15 +495,13 @@ int initSecurity(int* max_mem_lock, int*
     /* check that stderr, stdin and stdout are opened */
     /* NOTE: no file must be opened before this test! */
     /* Flawfinder: ignore */
-    canary = open("/dev/null", O_CREAT);
-    if ((canary >= 0) && (canary <= 2))
+    close (canary = dup(0));
+    if (canary != 3)
       {
         fprintf(stderr, "%s\n",
             _("stdin, stdout and/or stderr are invalid."));
-        close (canary);
         return 1;
       }
-    close (canary);
 
     return clearEnvironment();
   }