if a node sets exception handling - default values will affect streaming output

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### Dify version

1.16.1

### Cloud or Self Hosted

Self Hosted (Docker)

### Steps to reproduce

After setting the exception branch, no streaming output will be performed.

### ✔️ Expected Behavior

Normal flow of output content is proceeding.

### ❌ Actual Behavior

After setting the exception branch, no streaming output will be performed.

No file or test is named. Reproduce the self-hosted 1.16.1 workflow with an exception branch and compare streaming output with and without that branch, then trace the workflow streaming and exception-handling entry points. Done means normal output continues after the exception branch is configured, with a regression test covering the behavior.

Written by the indexing model from the issue text.