getTree causes crash on commits created by fileHistoryWalk

System information

• node version: v14.17.4
• npm or yarn version: Yarn v1.22.11
• OS/version/architecture: Debian 10 Buster x86_64
• Applicable nodegit version: 0.27.0

Problem

The getTree commit class method crashes when the commit is created by fileHistoryWalk.

This is technically a duplicate of #1045 but that was all the way back in 2016 and this problem has yet to be resolved.

Output:

(node:16430) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'getTree' of undefined
    at Commit.getTree (/home/hampus/loltest/lmao/node_modules/nodegit/dist/commit.js:290:20)
    at main (/home/hampus/loltest/lmao/index.js:16:34)
    at emitUnhandledRejectionWarning (internal/process/promises.js:168:15)
    at processPromiseRejections (internal/process/promises.js:247:11)
    at processTicksAndRejections (internal/process/task_queues.js:96:32)
(node:16430) TypeError: Cannot read property 'getTree' of undefined
    at Commit.getTree (/home/hampus/loltest/lmao/node_modules/nodegit/dist/commit.js:290:20)
    at main (/home/hampus/loltest/lmao/index.js:16:34)
(node:16430) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
    at emitDeprecationWarning (internal/process/promises.js:180:11)
    at processPromiseRejections (internal/process/promises.js:249:13)
    at processTicksAndRejections (internal/process/task_queues.js:96:32)

Recreating the bug

const nodegit = require("nodegit");

async function main() {
        const repository = await nodegit.Repository.openBare("{ repository }");

        const revw = nodegit.Revwalk.create(repository);

        revw.pushHead();

        const cnt = (await revw.getCommitsUntil(() => true)).length;

        revw.pushHead();

        const history = await revw.fileHistoryWalk("{ any file or folder }", cnt);
        for(const entry of history) {
                console.log(await entry.commit.getTree());
        }
}

main();

Workaround

A simple workaround for this is to create a new commit instance from the entry commit's sha.

const commit = await Commit.lookup(repository, entry.commit.sha());

// This will work
console.log(await commit.getTree());

Solution

#1110

Start with the getTree implementation shown in node_modules/nodegit/dist/commit.js and reproduce the failure through Revwalk.fileHistoryWalk in the issue's index.js example. Compare the failing entry.commit with the Commit.lookup workaround; done means getTree works directly on commits returned by fileHistoryWalk without crashing.