ID 496535 - Writer plug-ins in custom directories do not show in file type dropdown.

Problem summary
Writer plugins in custom directories do not show in file type dropdown

Customer reported version
nuke.12.2v7

Customer reported platform
windows10

Steps to reproduce

1. Move exrReader/Writer.{dll,so,dylib} to a temporary directory.

2. Launch Nuke.

3. Create a Write node

4. Check that the "exr" option is not available in the file type knob.

5. Remove the write node from the DAG.

6. Press 'X' in the DAG.

7. Type nuke.pluginAddPath('To/The/Temp/Dir')

8. Select python

9. Click ok

10. Create a new write node in the DAG.

11. Check that the file_type knob in the preferences panel does not have the EXR option.

Expected behavior
The Write node should include the custom plug-in file type in the dropdown knob.

Actual behavior
The custom plug-in file type is missing from the dropdown knob in the Write node.

Workaround
The workaround is to create the write node after the custom plugin path is added. Perhaps, the best place is init.py for this.

Reproduced by Developers in:
Nuke 13.1v1 - Windows 10

Nuke 12.2v9 - Windows 10