FIX: Member form validator fix.

[mfendeksilverstripe]

FIX: Member form validator fix.

Description

Fix for #11357

Manual testing steps

See #11357 for more details

Issues

• Member form validator doesn't work #11357

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[GuySartorelli]

The change looks good, thanks for submitting that.
Would you like to try adding a behat test for this, so we don't get the same regression again in the future?

That would need to target the silverstripe/silverstripe-admin repo.

[mfendeksilverstripe]

@GuySartorelli Added a unit test instead as a behat test seems like an overkill for this change.

[GuySartorelli]

That won't tells us that the validation works as expected - but it's a good step in the right direction and probably enough for this specific PR.
Cheers.

We're having some trouble with CI at the moment, but I've tested this locally and it works as expected so I'm happy to merge.

It'll be included in the October minor release (okay to slip in there since it's a bug fix - and probably better there than as a patch for 5.2 because the behavioral change is fairly substantial)