fix #68 ignore malformed date in {\info ..}

[r-Larch]

This PR fixes #68

If an {\info ..} contained a invalid date like: {\printim\yr0\mo0\dy0\hr0\min0} or {\creatim\yr0\mo0\dy0\hr0\min0}
then a System.ArgumentOutOfRangeException was thrown by the DateTime ctor.

This PR resolves the issue by ignoring the error since a malformed date can never be useful.

System.ArgumentOutOfRangeException Year, Month, and Day parameters describe an un-representable DateTime.
   at System.DateTime..ctor(Int32 year, Int32 month, Int32 day, Int32 hour, Int32 minute, Int32 second)
   at RtfPipe.Parser.ParseInfo(Document document, Group info)
   at RtfPipe.Parser.Parse()
   at RtfPipe.Rtf.ToHtml(RtfSource source, XmlWriter writer, RtfHtmlSettings settings)
   at RtfPipe.Rtf.ToHtml(RtfSource source, RtfHtmlSettings settings)

[lcocea]

Please release this fix at your earliest convenience, thank you.