C# language server assumes wrong solution path when Reload Window task executed

## Steps to reproduce

1. Execute task .NET: Open Solution. Choose a solution that is in a sub directory off root e.g. /feature/MyFeature.sln.
2. Notice the C# log windows picks up the correct solution path and loads all the projects successfully.
3. Now execute task Developer: Reload Window.
4. Notice the C# log window does not find the solution file - looks for /MyFeature.sln instead of feature/MyFeature.sln.

## Expected behavior
The path of the loaded solution in the C# Language Server is properly resolved when task Developer: Reload Window is executed.

## Actual behavior
The path of the loaded solution in the C# Language Server is NOT properly resolved when task Developer: Reload Window is executed.

## Additional context
Latest stable version of VSCode and C# extension running on Ubuntu.