[query] fix a bug when building histograms

[arnikola]

Fixes the histogram part of #2214

[codecov]

Codecov Report

Merging #2247 into master will decrease coverage by 0.1%.
The diff coverage is 87%.

@@           Coverage Diff            @@
##           master   #2247     +/-   ##
========================================
- Coverage    72.6%   72.5%   -0.2%     
========================================
  Files        1024    1024             
  Lines       89380   89086    -294     
========================================
- Hits        64917   64597    -320     
- Misses      20107   20132     +25     
- Partials     4356    4357      +1

Flag	Coverage Δ
#aggregator	82.1% <ø> (-0.1%)	⬇️
#cluster	62.5% <ø> (-22.7%)	⬇️
#collector	82.8% <ø> (ø)	⬆️
#dbnode	78.8% <ø> (-0.4%)	⬇️
#m3em	73.4% <ø> (-1%)	⬇️
#m3ninx	74.4% <ø> (ø)	⬆️
#m3nsch	58.4% <ø> (+7.2%)	⬆️
#metrics	17.5% <ø> (ø)	⬆️
#msg	74.8% <ø> (-0.2%)	⬇️
#query	69.3% <87%> (-0.1%)	⬇️
#x	83.1% <ø> (-0.1%)	⬇️

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