broadband-modem-mbim: fix task completion when peeking device fails
We cannot call peek_device() when we have already created a GTask for the async operation, because if the operation failed we would be completing the async operation with a totally different GTask than the one we had created ourselves, triggering memory leaks and leaving modem references around that should not exist (as the GTask we create holds a modem reference).
Issue found in the context of debugging this, may actually be fully related: