fix: ignore components which does not support DiscoInfo on determining MUC services at XMPP server

[pussbb]

Jitsi has speakerstats_component which is not support getting discoinfo and responses with

<iq xmlns="jabber:client" type="error" to="as@site.com/jsxc-6e71fee0" from="speakerstats.site.com" id="4bcd4257-0c2a-423a-b458-60b3d9079b8d:sendIQ">
<error type="cancel">
    <service-unavailable xmlns="urn:ietf:params:xml:ns:xmpp-stanzas"/>
</error>
</iq>

which is stopping searching for MUC component domain.

Following change set allows to ignore service-unavailable for components which does not support disco items request and will re-throw stanza item in something else happend.

[sualko]

According to XEP-0045: Multi-User Chat a MUC implementation MUST support Service Discovery (XEP-0030). Therefore we can safely ignore any failing disco request. Thanks for your pr.