Validate Date inputs to prevent infinite loops

[davidgoli]

Fixes #281.

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[codecov-io]

Codecov Report

Merging #282 into master will increase coverage by 0.06%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #282      +/-   ##
==========================================
+ Coverage   89.26%   89.32%   +0.06%     
==========================================
  Files          21       21              
  Lines        1900     1902       +2     
  Branches      567      572       +5     
==========================================
+ Hits         1696     1699       +3     
+ Misses        204      203       -1

Impacted Files	Coverage Δ
src/rrule.ts	98.23% <100%> (+0.02%)	⬆️
src/dateutil.ts	93.71% <100%> (+0.14%)	⬆️
src/parseoptions.ts	94.77% <100%> (+0.83%)	⬆️
src/masks.ts	100% <0%> (ø)	⬆️

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