bug: return error before creating multi pools if lbs is invalid to avoid leaks

[akshaynanavare]

1. Are you opening this pull request for bug-fixs, optimizations or new feature?

Yes, for small optimization of multi pools.

2. Please describe how these code changes achieve your intention.

If lbs is invalid then we should immediately return from NewMultiPool func instead of creating pool arrays and then check for lbs validation

3. Please link to the relevant issues (if any).

NA

4. Which documentation changes (if any) need to be made/updated because of this PR?

NA

4. Checklist

• I have squashed all insignificant commits.
• I have commented my code for explaining package types, values, functions, and non-obvious lines.
• I have written unit tests and verified that all tests passes (if needed).
• I have documented feature info on the README (only when this PR is adding a new feature).
• (optional) I am willing to help maintain this change if there are issues with it later.

[panjf2000]

I think you missed https://github.com/panjf2000/ants/blob/dev/multipool_func.go#L56-L58

[akshaynanavare]

I think you missed https://github.com/panjf2000/ants/blob/dev/multipool_func.go#L56-L58

@panjf2000 Yes, Added now. Thanks
UT is already there for both of the funcs
If you want explicitly to cover this code, I will add

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.30%. Comparing base (5c07bca) to head (7b5ec33).
Report is 3 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #317   +/-   ##
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  Coverage   91.30%   91.30%           
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  Files          11       11           
  Lines         759      759           
=======================================
  Hits          693      693           
  Misses         45       45           
  Partials       21       21           

Flag	Coverage Δ
unittests	91.30% <100.00%> (ø)

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[panjf2000]

LGTM
Thanks!