Fix a problem in syncLayerNodeEdits/syncLayersEvents

[jnwatson]

Once caught up and pending, those methods wouldn't yield a brand new layer's events until another after another event occured.

[codecov]

Codecov Report

Merging #1996 (5d7f06b) into master (53bee2f) will decrease coverage by 0.15%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1996      +/-   ##
==========================================
- Coverage   96.83%   96.67%   -0.16%     
==========================================
  Files         146      146              
  Lines       28585    28595      +10     
==========================================
- Hits        27679    27645      -34     
- Misses        906      950      +44     

Flag	Coverage Δ
linux	96.67% <100.00%> (-0.16%)	⬇️
linux_replay	?

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Impacted Files	Coverage Δ
synapse/cortex.py	95.98% <100.00%> (-0.77%)	⬇️
synapse/tests/utils.py	93.64% <0.00%> (-2.17%)	⬇️
synapse/lib/hiveauth.py	96.24% <0.00%> (-0.76%)	⬇️
synapse/lib/view.py	95.35% <0.00%> (-0.70%)	⬇️
synapse/lib/trigger.py	93.91% <0.00%> (-0.44%)	⬇️
synapse/lib/lmdbslab.py	99.40% <0.00%> (-0.20%)	⬇️
synapse/lib/layer.py	98.09% <0.00%> (-0.07%)	⬇️

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