[BUG] Non string in hashtag checking

[atrifat]

Issue

The following is bug in rare or edge case when hashtag extraction fail resulting undefined (non string) item. non string cannot be processed further resulting crash in application.

Stacktrace error message:

/app/nostr-filter/nostr-util.js:41
        const tag = hashtags[index].toLowerCase();
                                    ^

TypeError: Cannot read properties of undefined (reading 'toLowerCase')
    at hasNsfwHashtag (/app/nostr-filter/nostr-util.js:41:37)
    at WebSocket.<anonymous> (/app/nostr-filter/filter.js:942:78)

Solution

Wrap the implementation with String(tag) ensure that any non string value will be converted into string.