Demote error to warning on unbalanced markers

* Some markers from the application may be unbalanced, or it might be unbalanced
  if we began the capture with some markers already open (e.g. due to a push/pop
  around present).

renderdoc/driver/vulkan/vk_core.cpp

@@ -6144,7 +6144,7 @@ void WrappedVulkan::BakeEventNodes(ActionDescription &rootAction)
       {
         if(actionStack.count() == 0)
         {
-          RDCERR("Pop but the action stack is empty");
+          RDCWARN("Pop but the action stack is empty");
           parentAction = &rootAction;
         }
         else