Fix autocmddelete cannot remove webrequest event handler

Original code will overwrite the whole object if the same event
is regist even in different url pattern.

E.g:

```
autocmd BeforeRequest https://*/*?handler1 e=>({cancel:true})
autocmd BeforeRequest https://*/*?handler2 e=>({cancel:true})

" this will throw an error
autocmddelete BeforeRequest https://*/*?handler1
```

src/background/webrequests.ts

@@ -22,7 +22,8 @@ export const registerWebRequestAutocmd = (
     // I'm being lazy - strictly the functions map strings to void | blocking responses
     // eslint-disable-next-line @typescript-eslint/ban-types
     const listener = eval(func) as Function
-    LISTENERS[requestEvent] = { [pattern]: listener }
+    if (!LISTENERS[requestEvent]) LISTENERS[requestEvent] = {}
+    LISTENERS[requestEvent][pattern] = listener
     return browser.webRequest["on" + requestEvent].addListener(
         listener,
         { urls: [pattern] },