UdonSharp complains about not having any assemblies when there are no scripts in the project

[synergiance]

Describe the bug in detail: When I open the editor and there are no assemblies in the project, UdonSharp complains about not having assemblies when I've not clicked anything.

Provide steps/code to reproduce the bug:

• Create new fresh project with VRChat SDK and UdonSharp
• Close project
• Reopen Project
• Observe warning printed in console

Expected behavior: Nothing gets printed to console because UdonSharp hasn't been manually invoked to compile scripts that aren't there.

Additional Information: There should be a distinction between manually compiling all UdonSharp scripts, and when the editor/sdk decides it wants to check for script changes. If people manually tell UdonSharp to compile scripts and there are none, it should print this error, however, if people are just opening Unity, it should not.