fix: Don't set download state to Failure if message is available on another Session's transport (#7684)

[iequidoo]

Checked also manually in Desktop on top of 2631745. I.e. the bug is reproducible with pre-messages as well.

Fix #7684

[iequidoo]

test_transport_sync_new_as_primary failed: https://github.com/chatmail/core/actions/runs/21553875689/job/62107087345?pr=7794

...
        log.section("ac1_clone receives a message via the new primary transport")
        ac1_chat = ac1.create_chat(bob)
        ac1_chat.send_text("Hello!")
>       bob_chat_id = bob.wait_for_incoming_msg_event().chat_id
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

tests/test_multitransport.py:263: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
.tox/py/lib/python3.14/site-packages/deltachat_rpc_client/account.py:414: in wait_for_incoming_msg_event
    return self.wait_for_event(EventType.INCOMING_MSG)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.tox/py/lib/python3.14/site-packages/deltachat_rpc_client/account.py:35: in wait_for_event
    next_event = AttrDict(self._rpc.wait_for_event(self.id))
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.tox/py/lib/python3.14/site-packages/deltachat_rpc_client/rpc.py:173: in wait_for_event
    return queue.get()
           ^^^^^^^^^^^
/Library/Frameworks/Python.framework/Versions/3.14/lib/python3.14/queue.py:199: in get
    self.not_empty.wait()
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <Condition(<unlocked _thread.lock object at 0x10321ae90>, 0)>
timeout = None

    def wait(self, timeout=None):
        """Wait until notified or until a timeout occurs.
    
        If the calling thread has not acquired the lock when this method is
        called, a RuntimeError is raised.
    
        This method releases the underlying lock, and then blocks until it is
        awakened by a notify() or notify_all() call for the same condition
        variable in another thread, or until the optional timeout occurs. Once
        awakened or timed out, it re-acquires the lock and returns.
    
        When the timeout argument is present and not None, it should be a
        floating-point number specifying a timeout for the operation in seconds
        (or fractions thereof).
    
        When the underlying lock is an RLock, it is not released using its
        release() method, since this may not actually unlock the lock when it
        was acquired multiple times recursively. Instead, an internal interface
        of the RLock class is used, which really unlocks it even when it has
        been recursively acquired several times. Another internal interface is
        then used to restore the recursion level when the lock is reacquired.
    
        """
        if not self._is_owned():
            raise RuntimeError("cannot wait on un-acquired lock")
        waiter = _allocate_lock()
        waiter.acquire()
        self._waiters.append(waiter)
        saved_state = self._release_save()
        gotit = False
        try:    # restore state no matter what (e.g., KeyboardInterrupt)
            if timeout is None:
>               waiter.acquire()
E               Failed: Timeout (>300.0s) from pytest-timeout.
...
DEBUG    root:rpc.py:164 account_id=2 got an event {'kind': 'Info', 'msg': 'src/configure.rs:265: Configure ...'}
... (no logs with account_id=2 here)
========== ac1_clone receives a message via the new primary transport ==========
DEBUG    root:rpc.py:164 account_id=2 got an event {'kind': 'Info', 'msg': 'src/key.rs:331: Generating keypair.'}
DEBUG    root:rpc.py:164 account_id=2 got an event {'kind': 'AccountsItemChanged'}
DEBUG    root:rpc.py:164 account_id=2 got an event {'kind': 'Info', 'msg': 'src/key.rs:337: Keypair generated in 0s.'}
...

Not related to this PR of course. I.e. inner_configure() hung for bob.