Division By Zero errors being thrown by new BQ Source

Users are reporting issues with the BQ Source, where division by zero errors are being reported by Beam. A stack trace:
```

Log: [1] An exception was raised when trying to execute the workitem 2053702133423558223 : Traceback
(most recent call last): File "/usr/local/lib/python3.7/site-packages/dataflow_worker/batchworker.py",
line 649, in do_work work_executor.execute() File "/usr/local/lib/python3.7/site-packages/dataflow_worker/executor.py",
line 179, in execute op.start() File "dataflow_worker/native_operations.py", line 38, in dataflow_worker.native_operations.NativeReadOperation.start
File "dataflow_worker/native_operations.py", line 39, in dataflow_worker.native_operations.NativeReadOperation.start
File "dataflow_worker/native_operations.py", line 44, in dataflow_worker.native_operations.NativeReadOperation.start
File "dataflow_worker/native_operations.py", line 48, in dataflow_worker.native_operations.NativeReadOperation.start
File "/usr/local/lib/python3.7/site-packages/dataflow_worker/workercustomsources.py", line 69, in iter self._source.start_position,
self._source.stop_position) File "/usr/local/lib/python3.7/site-packages/apache_beam/io/concat_source.py",
line 78, in get_range_tracker start_position, stop_position, self._source_bundles) File "/usr/local/lib/python3.7/site-packages/apache_beam/io/concat_source.py",
line 131, in init self._compute_cumulative_weights(source_bundles[start[0]:last]) + [1] * File "/usr/local/lib/python3.7/site-packages/apache_beam/io/concat_source.py",
line 154, in _compute_cumulative_weights running_total.append(max(min_diff, min(1, running_total[-1]
+ w / total))) ZeroDivisionError: flo

```

I am suspecting this issue: https://issues.apache.org/jira/browse/BEAM-2716
[](https://issues.apache.org/jira/secure/AddComment!default.jspa?id=13341887)

Imported from Jira [BEAM-11497](https://issues.apache.org/jira/browse/BEAM-11497). Original Jira may contain additional context.
Reported by: pabloem.