make sure app_data is bytes, not str

[jardous]

Bugfix

LXMF.display_name_from_app_data() internally calls .decode() on its argument, which only works on bytes. In newer versions of RNS/LXMF, app_data can arrive (or be recalled) as a str instead of bytes, triggering the 'str' object has no attribute 'decode' error.

[jardous]

does not really solve the issue :/

[DEBUG] Received announce from with app_data: b'\x91\xa5Ditch'
[2026-03-15 21:01:18] [Error] Could not decode display name in included announce data. The contained exception was: 'str' object has no attribute 'decode'

Happens here:

    def register_announce_handler(self):
        """Register handler to capture display names from announces"""
        
        class LXMFPeerAnnounceHandler:
            def __init__(self, client):
                self.client = client
                self.aspect_filter = "lxmf.delivery"
            
            def received_announce(self, destination_hash, announced_identity, app_data):
                """Called when an LXMF delivery announce is received"""
                try:
                    if app_data:
                        print(f"\n[DEBUG] Received announce from {RNS.prettyhexrep(destination_hash)} with app_data: {app_data}")
                        if isinstance(app_data, str):
                            app_data = app_data.encode('utf-8')
                        display_name = LXMF.display_name_from_app_data(app_data)
                        
                        if display_name and isinstance(display_name, str):
                            hash_str = RNS.prettyhexrep(destination_hash)
                            clean_hash = hash_str.replace(":", "").replace(" ", "").lower()

[jardous]

ok - fixed the issue: https://github.com/markqvist/LXMF/compare/master...jardous:patch-1?expand=1

But no idea how to PR... :/