Merge pull request #21153 from amcasey/HardenNav154

Handle navigation to a doc ID without a corresponding doc

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.cs

@@ -997,6 +997,12 @@ internal override DocumentId GetDocumentIdInCurrentContext(DocumentId documentId
             }
 
             var hostDocument = GetHostDocument(documentId);
+            if (hostDocument == null)
+            {
+                // This can happen if the document was temporary and has since been closed/deleted.
+                return base.GetDocumentIdInCurrentContext(documentId);
+            }
+
             var itemId = hostDocument.GetItemId();
             if (itemId == (uint)VSConstants.VSITEMID.Nil)
             {