Remove potential space leak from Data.List.transpose

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I think some slowdown of the typical case is acceptable to prevent a space leak - which can be a major problem - on the basis that those seeking high performance will not be using lists in the first place. It's also fortunate that this is a small change and I appreciate that it comes with an explanatory comment.

I'm on this already, but could you perhaps add a test case that finds the space leak in the old code and is satisfied by the new code?

added core libraries label

Indeed it would be nice to have a testcase demonstrating the issue. Otherwise I have no objections.

approved this merge request

assigned to @marge-bot

I'll try to remember to get a test case written. Should be just a few lines, sticking an enormous list in the right spot and getting it retained. The tricky part will be making the problem apparent.

I will attempt to batch this MR (!3963 (closed))...

Merged in c30cc0e9

closed