Fatal error in hook_user_presave() when used with Role Delegation module

Patch #2 it's working for me.

From my point of view, the idea to use user_presave hook is wrong.
It's error-prone in many similar situations (i.e. #2646668: hook_user_presave).
Any validation of user_presave with order higher than module's one will get a fatal error.

My proposition is to move logic to change structure back into an array in the validate handler of form.

Tested patch with proof of concept in the attachment.

Re-roll patch with disabled testing - we have no tests for the module.

While not using the Role Delegation module as companion I was getting notices like
Notice: Undefined index: roles in single_user_role_user_presave() (line 81 ...
and observing that assigned single user roles got discarded on calling user_presave() in a custom module. This phenomenon is described in https://www.drupal.org/node/2646668 also.

Looking at the code, I changed line 78 from

if (!is_array($edit['roles'])) {

to

if (isset($edit['roles']) && !is_array(!empty($edit['roles']))) {

and got it working for my usecase.

Still, I think IRuslan is right to move the logic. Consequently, his patch #6 does also work.

I am seeing as variation of this issue and the patch at #6 does not help.

I am seeing anomalies and errors on the user registration page. See screenshot

@MrPaulDriver your issue seems to be little different and will be handled separately in https://www.drupal.org/project/single_user_role/issues/3012822