Merge pull request #583 from DomCR/issue-580_dxfclasses-dwgwriter-fix

Dwg DxfClasses writer fix

Author: DomCR

src/ACadSharp/IO/DWG/DwgStreamReaders/DwgClassesReader.cs

@@ -108,7 +108,7 @@ public DxfClassCollection Read()
 					this.notify($"Invalid DxfClass id value: {dxfClass.ItemClassId} for {dxfClass.CppClassName}", NotificationType.Error);
 				}
 
-				if (this._fileHeader.AcadVersion >= ACadVersion.AC1018)
+				if (this.R2004Plus)
 				{
 					//BL : Number of objects created of this type in the current DB(DXF 91).
 					dxfClass.InstanceCount = this._sreader.ReadBitLong();

src/ACadSharp/IO/DWG/DwgStreamWriters/DwgClassesWriter.cs

@@ -84,9 +84,9 @@ public void Write()
 					//BL : Number of objects created of this type in the current DB(DXF 91).
 					this._writer.WriteBitLong(c.InstanceCount);
 					//BS : Dwg Version
-					this._writer.WriteBitShort((short)this._document.Header.Version);
+					this._writer.WriteBitLong((short)this._document.Header.Version);
 					//BS : Maintenance release version.
-					this._writer.WriteBitShort(this._document.Header.MaintenanceVersion);
+					this._writer.WriteBitLong(this._document.Header.MaintenanceVersion);
 					//BL : Unknown(normally 0L)
 					this._writer.WriteBitLong(0);
 					//BL : Unknown(normally 0L)