Replace unwrap/expect when sending messages for IndexedDB

[rasviitanen]

Failing to send a message to the thread that starts a SyncOperation should not take down the whole idb thread, instead we should just fire some warnings using warn!.

To clarify

Change:
sender.send(result).unwrap() or sender.send(result).expect(...);

to something like this:

if sender.send(result).is_err() {
    warn!("Some Message");
}

Files:
components\net\indexeddb\idb_thread.rs