[MRG] BUG: Fix edge case with non existing connections in pick_connection()

[ntolley]

Closes #514. Fixes logic in pick_connection() where certain edge cases don't return an empty list even when the searched connection doesn't exist.

[ntolley]

@chenghuzi do you want to give a shot at reviewing this PR? I've added some tests to handle the edge case that you came across, but there may be others I haven't found on my own.

You can check this out locally with

git fetch upstream pull/515/head:fix_pick
git checkout fix_pick

[chenghuzi]

LGTM!

[chenghuzi]

Could we merge this now? As I'd like to integrate this into the new GUI asap so we can fix the corresponding GUI tests.

[ntolley]

Do you have merge permissions? If so make sure to do do a "Rebase and merge". Otherwise I'll let @jasmainak or @rythorpe go for it.

[jasmainak]

Thanks @ntolley and @chenghuzi !