Conversion from integer days to Portable Duration is bugged

[cpsusie]

This (demonstrative) unit test fails:

[Fact]
public void TestPortableDurationFromDaysAccuracy()  
{  
    int totalDays = -239805;   
    TimeSpan daysAsTs = TimeSpan.FromDays(totalDays);  
    PortableDuration fromTs = daysAsTs;  
    TimeSpan andBack = (TimeSpan)fromTs;  
    Assert.True(andBack == daysAsTs);  
    Int128 ticksPerSecond = 1_000_000_000;  
    //start with minute, then hour, then day  
    Int128 ticksPerDay = ticksPerSecond * 60; //per minute  
    ticksPerDay *= 60; //per hour  
    ticksPerDay *= 24; //per day  
    Assert.True(PortableDuration.TicksPerDay == ticksPerDay);  
    Int128 totalDaysInNanoSeconds = totalDays * ticksPerDay;  
    Int128 totalDaysInNanoSecondsFromDouble = (Int128)(((double)totalDays) * ((double)(long)ticksPerDay));  
    PortableDuration fromInt = PortableDuration.FromDays(totalDays);  
    Assert.True(fromInt == fromTs);  
}

Make it pass and find anything closely related.

[cpsusie]

NOTE: this bug was related to double conversion (FromDays) does not have an integer overload.