close channels when corresponding pipe is closed

[pfitzseb]

or an exception occurs.

This completely fixes julia-vscode/julia-vscode#1850 for me.

For every PR, please check the following:

• End-user documentation check. If this PR requires end-user documentation in the Julia VS Code extension docs, please add that at https://github.com/julia-vscode/docs.
• Changelog mention. If this PR should be mentioned in the CHANGELOG for the Julia VS Code extension, please open a PR against https://github.com/julia-vscode/julia-vscode/blob/master/CHANGELOG.md with those changes.

[codecov]

Codecov Report

Merging #48 (a21d5eb) into master (b347fbf) will increase coverage by 1.09%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #48      +/-   ##
==========================================
+ Coverage   90.50%   91.59%   +1.09%     
==========================================
  Files           4        4              
  Lines         200      226      +26     
==========================================
+ Hits          181      207      +26     
  Misses         19       19              

Flag	Coverage Δ
unittests	91.59% <100.00%> (+1.09%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/core.jl	86.61% <100.00%> (+1.34%)	⬆️
src/typed.jl	100.00% <0.00%> (ø)
src/interface_def.jl	100.00% <0.00%> (ø)

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