[Kotlin] fix invalid code when allOf is used

[etremblay]

#10792

I just backported the fix for updateModelForObject from CSharpNetCoreClientCodegen

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[etremblay]

Without this fix, this produced Animal() whish fail because Animal does not hava a constructor.

[etremblay]

@jimschubert (2017/09) heart, @dr4ke616 (2018/08) @karismann (2019/03) @Zomzog (2019/04) @andrewemery (2019/10) @4brunu (2019/11) @yutaka0m (2020/03)

[4brunu]

Looks good to me 👍