Fix total_doc synth population

[munrojm]

This PR fixes the bug mentioned in issue #309 with total_doc population when filters are included in addition to keywords.

[codecov-commenter]

Codecov Report

Merging #322 (ba2cd81) into main (0bbefea) will increase coverage by 56.70%.
The diff coverage is 79.32%.

@@             Coverage Diff             @@
##             main     #322       +/-   ##
===========================================
+ Coverage   32.39%   89.09%   +56.70%     
===========================================
  Files         109       59       -50     
  Lines        3084     1917     -1167     
===========================================
+ Hits          999     1708      +709     
+ Misses       2085      209     -1876     

Impacted Files	Coverage Δ
src/mp_api/__init__.py	100.00% <ø> (+43.47%)	⬆️
src/mp_api/routes/synthesis/data_adaptor.py	0.00% <0.00%> (ø)
src/mp_api/routes/synthesis/data_adaptor_synpro.py	0.00% <0.00%> (ø)
src/mp_api/routes/tasks/client.py	92.85% <ø> (+28.15%)	⬆️
src/mp_api/routes/dielectric/client.py	91.66% <50.00%> (+46.66%)	⬆️
src/mp_api/routes/molecules/client.py	90.32% <50.00%> (+51.03%)	⬆️
src/mp_api/routes/elasticity/client.py	93.93% <66.66%> (+59.45%)	⬆️
src/mp_api/routes/electrodes/client.py	87.50% <66.66%> (+37.50%)	⬆️
src/mp_api/routes/piezo/client.py	89.47% <66.66%> (+33.91%)	⬆️
src/mp_api/routes/robocrys/client.py	92.30% <66.66%> (+19.58%)	⬆️
... and 101 more

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