Throw NLogConfigurationException if TimeToSleepBetweenBatches <= 0

[304NotModified]

supersedes #1328

fixes #1069.

[codecov-io]

Current coverage is 75.17%

Merging #1336 into master will not affect coverage as of 0d104ea

@@            master   #1336   diff @@
======================================
  Files          267     267       
  Stmts        15524   15526     +2
  Branches      1632    1632       
  Methods          0       0       
======================================
+ Hit          11670   11672     +2
  Partial        383     383       
  Missed        3471    3471       

Review entire Coverage Diff as of 0d104ea

---

Uncovered Suggestions

1. +0.09% via ...gingConfiguration.cs#374...387
2. +0.09% via ...gingConfiguration.cs#340...353
3. +0.09% via ...argets/FileTarget.cs#1713...1725
4. See 7 more...

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