[query] return 0 if there was at least one valid number

[gediminasgu]

What this PR does / why we need it: PromQL compatibility fix. When running instant queries PromQL returns "0" in place of NaN if there was at least one valid number in a range. Otherwise, it returns "NaN". That is the fix for M3 query to behave in the same way.

Special notes for your reviewer: I'll change base branch to master when depending PR will be merged.

Does this PR introduce a user-facing and/or backwards incompatible change?:

NONE

Does this PR require updating code package or user-facing documentation?:

NONE

[codecov[bot]]

Codecov Report

Merging #2402 (83a36f7) into master (2c4f65c) will decrease coverage by 0.1%. Report is 1348 commits behind head on master. The diff coverage is 66.6%.

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #2402     +/-   ##
========================================
- Coverage    71.6%   71.6%   -0.1%     
========================================
  Files        1052    1052             
  Lines       93053   92934    -119     
========================================
- Hits        66702   66601    -101     
+ Misses      21891   21887      -4     
+ Partials     4460    4446     -14     

Flag	Coverage Δ
aggregator	76.4% <ø> (+<0.1%)	:arrow_up:
cluster	84.8% <ø> (ø)
collector	82.8% <ø> (ø)
dbnode	79.1% <ø> (+<0.1%)	:arrow_up:
m3em	74.4% <ø> (ø)
m3ninx	73.1% <ø> (ø)
m3nsch	51.1% <ø> (ø)
metrics	17.3% <ø> (ø)
msg	75.2% <ø> (ø)
query	67.9% <66.6%> (-0.2%)	:arrow_down:
x	81.8% <ø> (-0.1%)	:arrow_down:

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