fix: filter excel steps to nullify

[kevinkim-ogp]

Problem

Cannot transfer Pipe that contains Excel steps without connections.
Caused by inconsistent check for number of Excel steps to nullify.

How to replicate?
Create a Pipe with Excel step.
Transfer to user A (this works).
Don't do anything.
Transfer to user B (this will fail).

Solution

Only filter out Excel steps with connections.

Tests

1. Create a Pipe with Excel step.
2. Transfer to user A: this works
3. Don't do anything.
4. Transfer to user B: this should also work

[pregnantboy]

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