[Mac] Fixed `NRE` converting points from events.
[Mac] Fixed `NRE` converting points from events.

an NSView without a Window will cause `ConvertPointFromEvent` to throw a `NRE`, in this case is better just skip the BaseToScreen conversion.

mono/xwt,lytico/xwt,hwthomas/xwt,TheBrainTech/xwt,antmicro/xwt,hamekoz/xwt