BloombergLP::bdlt::Datetime::addMillisecondsIfValid

Add the specified number of milliseconds to the value of this object, adjusting the "date" part of the object accordingly, if the resulting value is in the valid range for a Datetime object. If 24 == hour() on entry, set the hour attribute to 0 before performing the addition. Return 0 on success, and a non‐zero value (with no effect) otherwise. Note that milliseconds may be positive, negative, or 0.