Fix aggregation metrics with zero tensors

[SkafteNicki]

What does this PR do?

Fixes #1063
Change if any(value) to if value.numel() != 0 to check if metric is empty.
Also adds the full_state_update to aggregation metrics as it was missing.

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• Did you write any new necessary tests?

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[codecov]

Codecov Report

Merging #1070 (7566fd9) into master (f0279bb) will increase coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #1070   +/-   ##
======================================
  Coverage      95%     95%           
======================================
  Files         181     181           
  Lines        8040    8046    +6     
======================================
+ Hits         7608    7614    +6     
  Misses        432     432