WebServiceTarget - Avoid re-throwing exceptions in async completion method

[snakefoot]

Attempt to resolve #2035

[codecov-io]

Codecov Report

Merging #2040 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #2040   +/-   ##
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  Coverage      82%     82%           
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  Files         286     286           
  Lines       19663   19663           
  Branches     2309    2309           
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  Hits        16042   16042           
  Misses       3056    3056           
  Partials      565     565

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[304NotModified]

Why do we need this? If throwexceptions is enabled, we like to get exceptions?

[snakefoot]

@304NotModified We like synchronous exceptions, but not the async ones that cannot be caught and crashes the application.

[304NotModified]

OK clear, thanks!