Fix autofilling when using multiple autofill fields

[hluchas]

Please be sure you are submitting this against the staging branch.

Q	A
Bug fix?	Y
New feature?
Automated tests included?	Y
Related user documentation PR URL
Related developer documentation PR URL
Issues addressed (#s or URLs)
BC breaks?
Deprecations?

Description: When using multiple checkbox groups or selects, only first one is autofilled.

Steps to reproduce the bug:

1. Create multiple Boolean or Select custom fields
2. Create form with checkbox groups mapping to those custom fields, using "Use assigned contact/company field's list choices. = Yes" in the Properties Tab
3. Add form to a landing page, then submit form with at least one of those checkboxes checked
4. Refresh landing page that the form is on

Steps to test this PR:

1. Load up this PR
2. Use reproduction steps

[escopecz]

@kuzmany @hluchas is this duplicate of #7347?

[kuzmany]

@escopecz yes it is, our #7347 fix radio + checkbox + some boolean unexpected autofill behaviour with it

[hluchas]

Funny, but OK. I would like to merge my PR naturally and because I've better division for alias _'.$alias.'_'., but @kuzmany has more fixed in it.

I don't know.

[kuzmany]

We're going to close 2.15.2 release, then I decide to close this PR favor to #7347
Better regex division could be submitted in another PR.