Fix package libs path in .Net project

Build couchbase-lite-net-3.1.0-82 contains couchbase-lite-net commit 300c217 with commit message:
Make sure items in path array are not null to cause argument null exception (#1406)

I was able to  repro the case in older .Net Core project application as well, so this is not a .Net 6 specific issue. The issue happens when the user moved the generated libs to a folder into a root directory ex. C:\folder or D:\folder.