staging/lustre/llite: protect from accessing NULL lli_clob

Need to check file's lli_clob object before calling
lov_read_and_clear_async_rc().
Signed-off-by: NBobi Jam <bobijam.xu@intel.com>
Reviewed-by: NJinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: NOleg Drokin <oleg.drokin@intel.com>
Reviewed-on: http://review.whamcloud.com/23031
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-8682Signed-off-by: NOleg Drokin <green@linuxhacker.ru>
Reviewed-by: NJames Simmons <jsimmons@infradead.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/llite/file.c

@@ -2328,9 +2328,11 @@ int ll_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 		lli->lli_async_rc = 0;
 		if (rc == 0)
 			rc = err;
-		err = lov_read_and_clear_async_rc(lli->lli_clob);
-		if (rc == 0)
-			rc = err;
+		if (lli->lli_clob) {
+			err = lov_read_and_clear_async_rc(lli->lli_clob);
+			if (rc == 0)
+				rc = err;
+		}
 	}
 
 	err = md_sync(ll_i2sbi(inode)->ll_md_exp, ll_inode2fid(inode), &req);