[TASK] Fix overriding of payment methods in getPaymentMethodList

[mashb1t]

Fixes Issue #13460, keeps changes from pull request #12284

Description

This fix only sets the value of a group if it doesn't already exist when calling \Magento\Payment\Helper\Data::getPaymentMethodList with parameter $withGroups = true.

Fixed Issues

#13460
#12284

Manual testing scenarios

1. Call method \Magento\Payment\Helper\Data::getPaymentMethodList
2. Value of group e.g. "offline" in $labelValues doesn't get set to null because there are already group-related values such as "checkmo".

[VladimirZaets]

Hi, @mash1t, I took your PR into processing, thank you for collaboration.

[magento-engcom-team]

@mash1t thank you for contributing. Please accept Community Contributors team invitation here to gain extended permissions for this repository.

[mashb1t]

@magento-engcom-team i am already a member of the magento team. What exactly did you mean by "extended permissions"?

[VladimirZaets]

@mash1t It's automated comment. extended permissions it's permissions that give the ability to Magento team for push to your branch.

[magento-engcom-team]

Hi @mash1t. Thank you for your contribution.
Changes from your Pull Request will be available with the upcoming 2.2.5 release.

[pascalhansjosten]

Hey @magento-engcom-team ,

i would like to ask if this fix is available on release 2.2.5?

Best regards,
Pascal Hansjosten