[BEAM-11578] Fix TypeError in dataflow_metrics has 0 distribution sum

[Abacn]

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[Abacn]

R: @y1chi

[y1chi]

LGTM

[Abacn]

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[codecov]

Codecov Report

Merging #17706 (d18c8b5) into master (da4fcad) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master   #17706   +/-   ##
=======================================
  Coverage   73.99%   73.99%           
=======================================
  Files         695      695           
  Lines       91798    91798           
=======================================
+ Hits        67926    67928    +2     
+ Misses      22624    22622    -2     
  Partials     1248     1248           

Flag	Coverage Δ
python	83.74% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...n/apache_beam/runners/dataflow/dataflow_metrics.py	74.83% <100.00%> (ø)
sdks/python/apache_beam/io/gcp/bigquery.py	64.99% <0.00%> (-0.12%)	⬇️
sdks/python/apache_beam/transforms/core.py	92.30% <0.00%> (ø)
...hon/apache_beam/runners/worker/bundle_processor.py	93.55% <0.00%> (+0.12%)	⬆️
...ks/python/apache_beam/runners/worker/sdk_worker.py	89.09% <0.00%> (+0.15%)	⬆️
sdks/python/apache_beam/utils/interactive_utils.py	97.56% <0.00%> (+2.43%)	⬆️

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