fix(cornerstoneTools):Fetch the overlay if an async method is available

[wayfarer3130]

This fix allows the overlay tool to call an asynchronous retrieveBulkData method if the overlay pixeldata has a retrieveBulkData method, and then render the overlay correctly.

[codecov[bot]]

Codecov Report

Merging #1451 (80bc9e2) into master (95c3b7c) will decrease coverage by 0.05%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #1451      +/-   ##
==========================================
- Coverage   20.16%   20.10%   -0.06%     
==========================================
  Files         287      287              
  Lines       10102    10131      +29     
  Branches     2060     2069       +9     
==========================================
  Hits         2037     2037              
- Misses       6852     6872      +20     
- Partials     1213     1222       +9     

Impacted Files	Coverage Δ
src/tools/OverlayTool.js	1.16% <0.00%> (-0.60%)	:arrow_down:

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