Add a filter to exclude groups that don't have a project node at all.

Author: bclothier

Rubberduck.Core/Navigation/CodeExplorer/CodeExplorerViewModel.cs

@@ -293,6 +293,7 @@ private void HandleStateChanged(object sender, ParserStateEventArgs e)
 
             var userDeclarations = _state.DeclarationFinder.AllUserDeclarations
                 .GroupBy(declaration => declaration.ProjectId)
+                .Where(grouping => grouping.Any(declaration => declaration.DeclarationType == DeclarationType.Project))
                 .ToList();
 
             if (userDeclarations.Any(