Require a valid index when setting value

[passsy]

• KtMutableIterator.set throw IndexOutOfBoundsException when next() wasn't called

[codecov]

Codecov Report

Merging #69 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master     #69      +/-   ##
=========================================
+ Coverage    99.7%   99.7%   +<.01%     
=========================================
  Files          40      40              
  Lines        1696    1697       +1     
=========================================
+ Hits         1691    1692       +1     
  Misses          5       5

Impacted Files	Coverage Δ
lib/src/collection/impl/iterator.dart	100% <100%> (ø)	⬆️

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