[Bug] Errors in nested subgraphs sometimes do not raise an error dialog or show an error status (red outline) on violating node

When running this workflow:

- [nested execution bug.json](https://github.com/user-attachments/files/21607075/nested.execution.bug.json)

Since the latent samples is not connected to the Decode node on the 3rd level (where level 1 is root, 2nd level is inside subgraph, 3rd level is subgraph inside subgraph), it should properly raise an error (which will result in the "prompt execution failed" dialogue and an error message in the console). Instead, it just silently fails with no further steps.

Also tested with just two subgraphs and 1 sampler:

- [nested execution bug (2).json](https://github.com/user-attachments/files/21607093/nested.execution.bug.2.json)

and it provides the appropriate pop-up and console log to show what inputs are missing.

This can be quite problematic for users, if they make small mishaps in the workflow itself. Note: there should also be the normal red circle over the inputs thats missing, upon failed execution

Related:

- https://github.com/Comfy-Org/ComfyUI_frontend/issues/4621

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-4689-Bug-Errors-in-nested-subgraphs-sometimes-do-not-raise-an-error-dialog-or-show-an-err-2466d73d365081bb98ffeb61d4da1ead) by [Unito](https://www.unito.io)