pty.c: more difensive

* ext/pty/pty.c (chfunc): should not close the slave fd if it is 0..2.
  [ruby-core:89043] [Bug #15116]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64766 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ext/pty/pty.c

@@ -143,7 +143,7 @@ chfunc(void *data, char *errbuf, size_t errbuf_len)
     dup2(slave,0);
     dup2(slave,1);
     dup2(slave,2);
-    close(slave);
+    if (slave < 0 && slave > 2) (void)!close(slave);
 #if defined(HAVE_SETEUID) || defined(HAVE_SETREUID) || defined(HAVE_SETRESUID)
     if (seteuid(getuid())) ERROR_EXIT("seteuid()");
 #endif