NTFS: Do not dereference pointer before checking for NULL.

Found by Coverity software (http://scan.coverity.com).
Signed-off-by: Anton Altaparmakov <anton@tuxera.com>

fs/ntfs/attrib.c

 /**
  * attrib.c - NTFS attribute operations.  Part of the Linux-NTFS project.
  *
- * Copyright (c) 2001-2007 Anton Altaparmakov
+ * Copyright (c) 2001-2012 Anton Altaparmakov and Tuxera Inc.
  * Copyright (c) 2002 Richard Russon
  *
  * This program/include file is free software; you can redistribute it and/or
@@ -345,10 +345,10 @@ LCN ntfs_attr_vcn_to_lcn_nolock(ntfs_inode *ni, const VCN vcn,
 	unsigned long flags;
 	bool is_retry = false;
 
+	BUG_ON(!ni);
 	ntfs_debug("Entering for i_ino 0x%lx, vcn 0x%llx, %s_locked.",
 			ni->mft_no, (unsigned long long)vcn,
 			write_locked ? "write" : "read");
-	BUG_ON(!ni);
 	BUG_ON(!NInoNonResident(ni));
 	BUG_ON(vcn < 0);
 	if (!ni->runlist.rl) {
@@ -469,9 +469,9 @@ runlist_element *ntfs_attr_find_vcn_nolock(ntfs_inode *ni, const VCN vcn,
 	int err = 0;
 	bool is_retry = false;
 
+	BUG_ON(!ni);
 	ntfs_debug("Entering for i_ino 0x%lx, vcn 0x%llx, with%s ctx.",
 			ni->mft_no, (unsigned long long)vcn, ctx ? "" : "out");
-	BUG_ON(!ni);
 	BUG_ON(!NInoNonResident(ni));
 	BUG_ON(vcn < 0);
 	if (!ni->runlist.rl) {