Converting Texture Objects to Texture Object Parameters loses reference to texture

This issue can cause some workflow problems when a user is creating materials using texture objects, then decides to expose those objects as parameters. It can be worked around if the user is aware of the problem, but it can still cause lost work and/or time.

1. Create a new material
2. In that material, create a Texture Object node
3. Set the "Texture" value of the node to something other than DefaultTexture
4. Right-click on the Texture Object node and select "Convert to Parameter"
5. Click on the Texture Object Parameter node and note that the Texture value has been reverted to DefaultTexture.