freevxfs: possible null pointer dereference fix

sb_read may return NULL, so let's explicitly check it.

Signed-off-by: Dmitriy Monakhov <dmonakhov@openvz.org>
Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/freevxfs/vxfs_inode.c b/fs/freevxfs/vxfs_inode.c
index 098a915..d1f7c5b 100644
--- a/fs/freevxfs/vxfs_inode.c
+++ b/fs/freevxfs/vxfs_inode.c
@@ -99,7 +99,7 @@
 	offset = ((ino % (sbp->s_blocksize / VXFS_ISIZE)) * VXFS_ISIZE);
 	bp = sb_bread(sbp, block);
 
-	if (buffer_mapped(bp)) {
+	if (bp && buffer_mapped(bp)) {
 		struct vxfs_inode_info	*vip;
 		struct vxfs_dinode	*dip;