Fix bug in method AR TimeZoneConverter#set_time_zone_without_conversion

[alpaca-tc]

Summary

Multi-parameter attributes conversion with invalid params doesn't work when time_zone_aware_attributes is enabled, because when invalid params is given to Multi-parameter attributes conversion, set_time_zone_without_conversion is assigned to nil.

[rails-bot]

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[rafaelfranca]

Could you add a CHANGELOG entry?

[alpaca-tc]

@rafaelfranca 👍

[rafaelfranca]

Could you squash your commits?

[alpaca-tc]

@rafaelfranca i see 😄

[alpaca-tc]

@rafaelfranca 👍