Fix PresentationBuilder resource leak

[Lotes]

You need to dispose the stream. Otherwise when two parts use the same resource it will complain about multiple opened streams when package is in "UpdateMode". This change was done on top of Pullrequest #15.

[Lotes]

One possible stacktrace... My fix closes about 12 leaks. I have only one path here.

 ---> System.IO.IOException: Entries cannot be opened multiple times in Update mode.
   at System.IO.Compression.ZipArchiveEntry.OpenInUpdateMode()
   at System.IO.Packaging.ZipStreamManager.Open(ZipArchiveEntry zipArchiveEntry, FileMode streamFileMode, FileAccess streamFileAccess)
   at System.IO.Packaging.ZipPackagePart.GetStreamCore(FileMode streamFileMode, FileAccess streamFileAccess)
   at System.IO.Packaging.PackagePart.GetStream(FileMode mode, FileAccess access)
   at OpenXmlPowerTools.PresentationBuilder.CopyExtendedPart(OpenXmlPart oldContentPart, OpenXmlPart newContentPart, XElement extendedReference, XName attributeName)
   at OpenXmlPowerTools.PresentationBuilder.CopyRelatedPartsForContentParts(PresentationDocument newDocument, OpenXmlPart oldContentPart, OpenXmlPart newContentPart, IEnumerable`1 newContent, List`1 images, List`1 mediaList)
   at OpenXmlPowerTools.PresentationBuilder.AppendSlides(PresentationDocument sourceDocument, PresentationDocument newDocument, Int32 start, Int32 count, Boolean keepMaster, List`1 images, SlideMasterPart currentMasterPart, List`1 mediaList)
   at OpenXmlPowerTools.PresentationBuilder.BuildPresentation(List`1 sources, PresentationDocument output)
   at OpenXmlPowerTools.PresentationBuilder.BuildPresentation(List`1 sources)

[hbnrmx]

@Lotes thanks for saving me some work with your fix!

Since this fork doesn't seem to be maintained, is there any chance we could direct your fix towards another actively maintained fork?

Looking over the forks, I see that https://github.com/Codeuctivity/OpenXmlPowerTools might be a candidate. @stesee could you shed some light on the status of that fork and its willingness to accept other PRs? Thank you!

[stesee]

Status: Pet Project
Would I accept PRs? Sure. As long as they add tests for new functionality and the effort fits into pet project budget.

[hbnrmx]

FYI, we decided to go a different route but I appreciate your quick responses. Thank you guys!