Fix missing $joinMap in AbstractQueryConverter

[sad270]

In AbstractQueryConverter::getParentJoinIdForVirtualColumnJoin method, $joinMap variable is missing.
So we never enter in last elseif isset($joinMap[$parentAlias]['processed'])
And when we have 2 joins in a virtual_fields the second join is not added in DQL

Example:

# src/Oro/Bundle/AccountBundle/Resources/config/oro/entity.yml
oro_entity:
    virtual_fields:
        Oro\Bundle\AccountBundle\Entity\Account:
            contactInformation:
                query:
                    select:
                        expr:         emails.email
                        return_type:  string
                    join:
                        left:
                            - { join: entity.defaultContact, alias: defaultContact }
                            - { join: defaultContact.emails, alias: emails, conditionType: 'WITH', condition: 'emails.primary = true' }

Need for fix this oroinc/crm#346

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