udf: Return -ENOMEM when allocation fails in udf_get_filename()

Return -ENOMEM when allocation fails in udf_get_filename(). Update
udf_pc_to_char(), udf_readdir(), and udf_find_entry() to handle the
error appropriately. This allows us to pass appropriate error to
userspace instead of corrupting symlink contents by omitting some path
elements.

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/namei.c

@@ -234,7 +234,7 @@ static struct fileIdentDesc *udf_find_entry(struct inode *dir,
 			continue;
 
 		flen = udf_get_filename(sb, nameptr, lfi, fname, UDF_NAME_LEN);
-		if (flen && udf_match(flen, fname, child->len, child->name))
+		if (flen > 0 && udf_match(flen, fname, child->len, child->name))
 			goto out_ok;
 	}