bug: `ERROR loading NDKInstance` if relay is unreachable

[theborakompanioni]

If one of the given relays in NDKProvider.relayUrls is not reachable, an error is thrown:

ERROR loading NDK NDKInstance undefined

Expected behaviour

NDK can be used without a connection to the defunct relay.

Actual behaviour

NDK cannot be used at all and is undefined.

How to reproduce

Add wss://non-existing-relay.example.com to the NDKProvider:

<NDKProvider
  relayUrls={[
    "wss://non-existing-relay.example.com",
    "wss://relay.damus.io",
    "wss://relay.snort.social",
    "wss://purplepag.es",
  ]}
>
   [...]
</NDKProvider>