Fix interface conversion from int types to float64

[shrdlu68]

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[suzuki-shunsuke]

Can we get a chance to review this pull request?
I wrote an issue about this pull request.

• INTERNAL ERROR: (CRASH) interface conversion: interface {} is int, not float64 #752

[suzuki-shunsuke]

I'm not sure why we need to convert the value to int64.

Is the following code wrong?

return makeDoubleCheck(i, float64(v))

[suzuki-shunsuke]

I see.

makeDoubleCheck(i, float64(v)) causes a compile error.

cannot convert v (variable of type interface{}) to type float64: need type assertion

[suzuki-shunsuke]

I'm trying this pull request, but this doesn't work as expected.
panic doesn't occur but the return value is always 0.

[sbarzowski]

Closing in favour of #753