Btrfs: adjust NULL test

Move the call to BUG_ON to before the dereference of the tested value.
Signed-off-by: NJulia Lawall <julia@diku.dk>
Signed-off-by: NChris Mason <chris.mason@oracle.com>

fs/btrfs/inode.c

@@ -2607,8 +2607,8 @@ noinline int btrfs_truncate_inode_items(struct btrfs_trans_handle *trans,
 	if (root->ref_cows)
 		btrfs_drop_extent_cache(inode, new_size & (~mask), (u64)-1, 0);
 	path = btrfs_alloc_path();
-	path->reada = -1;
 	BUG_ON(!path);
+	path->reada = -1;
 
 	/* FIXME, add redo link to tree so we don't leak on crash */
 	key.objectid = inode->i_ino;