fix: prevent crashing the rest process (#2159)

* fix: prevent crashing the rest process

There where instances where some requests crashed the rest process. I found that checking for a body pretty much fixed it. 
There is probably a better way to do this, please improve this if you have an idea :)

* chore: use undefined instead of empty string

Co-authored-by: LTS20050703 <87189679+lts20050703@users.noreply.github.com>

* chore: use ternary operator

Co-authored-by: LTS20050703 <87189679+lts20050703@users.noreply.github.com>

template/bigbot/src/rest/mod.ts

@@ -42,7 +42,7 @@ async function handleRequest(conn: Deno.Conn) {
       );
     }
 
-    const json = (await requestEvent.request.json());
+    const json = requestEvent.request.body ? (await requestEvent.request.json()) : undefined;
 
     try {
       const result = await rest.runMethod(