re-fix of old silent error (loss shape broadcast mismatch caused by extra dim of size 1)

[shreyasc30]

had to re-fix the gating error after recent changes, now convergence (or anything of size (b, h, w, 1)) is correctly squeezed before being gated even in the absence of n_sources

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.22%. Comparing base (e9de7ce) to head (2eadbf5).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1063      +/-   ##
==========================================
+ Coverage   81.21%   81.22%   +0.01%     
==========================================
  Files          23       23              
  Lines        3045     3047       +2     
==========================================
+ Hits         2473     2475       +2     
  Misses        572      572              

Flag	Coverage Δ
unittests	81.22% <100.00%> (+0.01%)	⬆️

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