MgMultiGeometry::Deserialize doesn't work with MgAgfStream

[waltweltonlair]

The following code currently fails:

    Ptr<MgMultiGeometry> geom = ...;

    MgAgfReaderWriter agfReaderWriter;
    Ptr<MgByteReader> reader = agfReaderWriter.Write(geom);
    Ptr<MgGeometry> multiGeometry = agfReaderWriter.Read(reader);

The MgAgfReaderWriter::Read call results in a call to MgMultiGeometry::Deserialize with an MgAgfStream, but Deserialize is not correctly handling this case.

[waltweltonlair]

This is a regression introduced with changeset r3502 to fix ticket #788.

In that submission special code was added to get the geometry type via a peek operation. The peek operation was coded to work with MgStream, but it doesn't work with MgAgfStream.

MgStream inherits from MgStreamReader / MgStreamWriter, and the default implementations of the Get / Write methods in MgStreamReader / MgStreamWriter serialize stream header / version / data header fields. The peek operation added in r3502 was coded to handle this.

MgAgfStream inherits from MgStream and overrides the Get / Write methods. It does not serialize stream header / version / data header fields.

To fix this we simply need to enhance the code in MgMultiGeometry::Deserialize to check the type of the passed-in MgStream. If it's an MgAgfStream then we need to use the original pre-3502 code for doing the peek operation. If it's a pure MgStream then we use the code added in r3502.

[waltweltonlair]

Fixed in the trunk stream with changeset r7238.

Fixed in the 2.5k sandbox stream with changeset r7239.