Fix: Linux build error in previous commit

Faulty commit is 9c79acf9b

Pull Request: https://projects.blender.org/blender/blender/pulls/125119

source/blender/editors/sculpt_paint/sculpt.cc

@@ -946,6 +946,8 @@ bool vert_is_boundary(const Span<bool> /*hide_poly*/,
     case SUBDIV_CCG_ADJACENT_NONE:
       return false;
   }
+  BLI_assert_unreachable();
+  return false;
 }
 
 bool vert_is_boundary(BMVert *vert)