Share folder failed on readonly storage

[pulcov]

It is impossible to share folder with external user if folder is readonly. No error occurs if this action is done with a file.

Steps to reproduce

1. Set external storage to readonly
2. Select folder on readonly storage and share it with external user (e-mail address)

Expected behaviour

Folder is shared and external user get an e-mail with link

Actual behaviour

Error : Can't increase permissions of ....

Server configuration

**Nextcloud version: 13.0.4

[MorrisJobke]

cc @nextcloud/sharing @icewind1991

[rullzer]

This is fixed in 14 I think.

[MorrisJobke]

Then let's close it for 14 and if there are still edge cases we can look into them.