Do not show an error on completion eval if the program is not installed

[tiangolo]

✨ Do not show an error on completion eval if the program is not installed

[github-actions]

🚀 Deployed on https://5e809e86bbc7525000ce2e6a--typertiangolo.netlify.com

[github-actions]

🚀 Deployed on https://5e80a3d575aa64714a07116e--typertiangolo.netlify.com

[codecov-io]

Codecov Report

Merging #83 into master will not change coverage by %.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #83   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          214       214           
  Lines         4001      4001           
=========================================
  Hits          4001      4001           

Impacted Files	Coverage Δ
.../test_completion/test_completion_install_source.py	100.00% <ø> (ø)
tests/test_completion/test_completion.py	100.00% <100.00%> (ø)
tests/test_completion/test_completion_install.py	100.00% <100.00%> (ø)
typer/completion.py	100.00% <100.00%> (ø)

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