Null-checks PR Body in removeGuideComments (#71043)

This is what #71041 was supposed to be.

## About The Pull Request
Hey there,

I was looking at #71028, and I noticed that this workflow failed because
oranges left the PR body blank. I think that's silly, so let's just
include an early return so the whole thing doesn't throw.

This is the error:


![image](https://user-images.githubusercontent.com/34697715/199852746-24b2ed53-442d-4c40-b81d-902236183328.png)
via:
https://github.com/tgstation/tgstation/actions/runs/3382875608/jobs/5618241641

Here's an example PR where I fixed it (on my fork, just expand the
"Remove guide comments" step):
https://github.com/san7890/bruhstation/actions/runs/3389994395/jobs/5633658300

## Why It's Good For The Game

It hurts my heart to see checks red out in trivial situations like this.
## Changelog
Literally nothing here concerns players.

Ignore the commit history I was testing this PR the wrong way and was
effectively gaslighting myself (we're good now though)

tools/pull_request_hooks/removeGuideComments.js

@@ -18,6 +18,11 @@ function escapeRegex(string) {
 export async function removeGuideComments({ github, context }) {
   let newBody = context.payload.pull_request.body;
 
+  if (!newBody) {
+	console.log("PR body is empty, skipping...");
+	return;
+  }
+
   for (const comment of comments) {
     newBody = newBody.replace(
       new RegExp(`^\\s*${escapeRegex(comment)}\\s*`, "gm"),