From: Johannes Schindelin <johannes.schindelin@gmx.de>

In 9fefce68dc8 (merge-ort: basic outline for merge_switch_to_result(),
2020-12-13), we added functionality to lay down the result of a merge on
disk. But we forgot to release the data structures in case
`unpack_trees()` failed to run properly.

This was pointed out by the `linux-leaks` job in our CI runs.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Submitted-As: https://lore.kernel.org/git/pull.1307.git.1659084748350.gitgitgadget@gmail.com