Make lmdbslab optsfile updates only when the yamlload result is safe to use.

[vEpiphyte]

No description provided.

[codecov]

Codecov Report

Merging #2694 (1770bd1) into master (30ff9c5) will decrease coverage by 0.11%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2694      +/-   ##
==========================================
- Coverage   96.94%   96.83%   -0.12%     
==========================================
  Files         206      206              
  Lines       39769    39771       +2     
==========================================
- Hits        38555    38512      -43     
- Misses       1214     1259      +45     

Flag	Coverage Δ
linux	96.83% <100.00%> (+<0.01%)	⬆️
linux_replay	?

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Impacted Files	Coverage Δ
synapse/lib/lmdbslab.py	99.71% <100.00%> (+0.19%)	⬆️
synapse/tests/utils.py	93.69% <0.00%> (-1.98%)	⬇️
synapse/lib/hiveauth.py	95.37% <0.00%> (-0.69%)	⬇️
synapse/cortex.py	96.54% <0.00%> (-0.66%)	⬇️
synapse/lib/view.py	96.75% <0.00%> (-0.49%)	⬇️
synapse/lib/trigger.py	94.98% <0.00%> (-0.39%)	⬇️
synapse/lib/jsonstor.py	98.30% <0.00%> (-0.25%)	⬇️
synapse/lib/layer.py	97.06% <0.00%> (-0.13%)	⬇️

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