VS: Fix regression in C# source links
Fix logic used since !4374 (merged). Add a check of the physical file location for C# source groups.
Fixes: #21221 (closed)
Backport: release
Topic-rename: csharp-source_group-bugfix
Edited by Brad King
Fix logic used since !4374 (merged). Add a check of the physical file location for C# source groups.
Fixes: #21221 (closed)
Backport: release
Topic-rename: csharp-source_group-bugfix