Correctly handle -epoch time values when converting from JS time to base::Time
-11644473600 seconds (which represents windows epoch time of
this value is internally represented by 0 which is mistakenly confused with a
null time value.
for which 0 or -epoch do not represent null values. So the extra check was
* In fact there is a comment in FromJsTime method making it clear that 0 is a
valid value but this was missed in ToJsTime method.