2.x: Fix zip not stopping the subscription upon eager error

[akarnokd]

The Observable.zip did not stop subscribing to the next sources if the previous one failed with an onError. Flowable.zip works as intended.

Fixes #6487

[codecov]

Codecov Report

Merging #6488 into 2.x will decrease coverage by 0.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##                2.x    #6488      +/-   ##
============================================
- Coverage     98.26%   98.25%   -0.02%     
- Complexity     6297     6298       +1     
============================================
  Files           675      675              
  Lines         45159    45163       +4     
  Branches       6244     6244              
============================================
- Hits          44374    44373       -1     
- Misses          244      247       +3     
- Partials        541      543       +2

Impacted Files	Coverage Δ	Complexity Δ
...x/internal/operators/observable/ObservableZip.java	100% <100%> (ø)	6 <0> (ø)	⬇️
.../operators/flowable/FlowableBlockingSubscribe.java	93.02% <0%> (-4.66%)	10% <0%> (-1%)
...nternal/operators/parallel/ParallelReduceFull.java	91.08% <0%> (-3.97%)	2% <0%> (ø)
...ternal/operators/observable/ObservablePublish.java	94.69% <0%> (-3.54%)	11% <0%> (ø)
...ernal/operators/flowable/FlowableFromIterable.java	95.18% <0%> (-2.68%)	5% <0%> (ø)
...ternal/operators/completable/CompletableMerge.java	96.42% <0%> (-2.39%)	2% <0%> (ø)
...activex/internal/schedulers/ScheduledRunnable.java	98.07% <0%> (-1.93%)	29% <0%> (-1%)
...internal/operators/flowable/FlowableSwitchMap.java	95.28% <0%> (-1.42%)	3% <0%> (ø)
.../io/reactivex/internal/schedulers/IoScheduler.java	89.36% <0%> (-1.07%)	9% <0%> (ø)
...ernal/operators/flowable/FlowableFlatMapMaybe.java	91.78% <0%> (-0.97%)	2% <0%> (ø)
... and 20 more

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