imresize: handle 0-parameter colorant types

[johnnychen94]

fixes #97

[codecov]

Codecov Report

Merging #126 (fa9cdfe) into master (b195f34) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #126      +/-   ##
==========================================
+ Coverage   93.86%   93.90%   +0.03%     
==========================================
  Files           8        8              
  Lines         326      328       +2     
==========================================
+ Hits          306      308       +2     
  Misses         20       20              

Impacted Files	Coverage Δ
src/resizing.jl	98.80% <100.00%> (+0.01%)	⬆️

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