decoding: fix decoding of large events like nostr reports

I was trying to do an initial malloc that was somewhat efficient. Looks
like our ndb_builder needs a bit more space when allocating the
ndb_note.

Changelog-Fixed: Fixed nostr reporting decoding

damus/Nostr/NostrResponse.swift

@@ -39,7 +39,7 @@ enum NostrResponse {
 
     static func owned_from_json(json: String) -> NostrResponse? {
         return json.withCString{ cstr in
-            let bufsize: Int = max(Int(Double(json.utf8.count) * 2.0), Int(getpagesize()))
+            let bufsize: Int = max(Int(Double(json.utf8.count) * 4.0), Int(getpagesize()))
             let data = malloc(bufsize)
 
             if data == nil {