[Bug]: LogEntries for exceptions do not include the transform_id

### What happened?

In normal operation the [StateSampler](https://github.com/apache/beam/blob/master/sdks/python/apache_beam/runners/worker/statesampler_slow.py#L108) keeps track of the currently executing step in a stack. When a log is emitted, it [looks](https://github.com/apache/beam/blob/master/sdks/python/apache_beam/runners/worker/log_handler.py#L147) at the [top](https://github.com/apache/beam/blob/master/sdks/python/apache_beam/runners/worker/statesampler_slow.py#L41) of the stack for the current step. However, during an exception, this exits the StateSampler scope and pops off the current step and either gets the incorrect step or does not have any step in the stack.

Potential fix would be to only pop the stack when there is no exception.

### Issue Priority

Priority: 2 (default / most bugs should be filed as P2)

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