Nullish Coalescing operator - functions shouldn't be evaluated multiple times

[0xe]

Spec clearly says to evaluate the CoalesceExpression once:

https://tc39.es/ecma262/multipage/ecmascript-language-expressions.html#prod-CoalesceExpression

CoalesceExpression : CoalesceExpressionHead ?? BitwiseORExpression

1. Let lRef be ? Evaluation of CoalesceExpressionHead.
2. Let lVal be ? GetValue(lRef).
3. If lVal is either undefined or null, then
   a. Let rRef be ? Evaluation of BitwiseORExpression.
   b. Return ? GetValue(rRef).
4. Else,
   a. Return lVal.

Yet, we generate tree like this, that evaluates it multiple times.

    VAR 2
        NAME eval1 2
            HOOK
                OR
                    SHEQ
                        NULL
                        CALL 2
                            NAME f 2
                    SHEQ
                        NAME undefined
                        CALL 2
                            NAME f 2
                NUMBER 42.0 2
                CALL 2
                    NAME f 2

I'm working on fixing this. (Thanks @andreabergia for noticing!)