message: [mdns-avahi] fix potential crash on browsing
  This commit fixes a bug that `aName` is `nullptr` when `aEvent` is not
  `AVAHI_BROWSER_NEW`. So, we should only use `aName` on
  `AVAHI_BROWSER_NEW`.
diff: @@ -1005,16 +1005,25 @@ void PublisherAvahi::ServiceSubscription::HandleBrowseResult(AvahiServiceBrowser
  assert(mServiceBrowser == aServiceBrowser);
  - otbrLogInfo("browse service reply: %s.%s inf %u, flags=%u", aName, aType, aInterfaceIndex, aFlags);
  + otbrLogInfo("browse service reply: %s.%s inf %u, event=%d, flags=%u", aName, aType, aInterfaceIndex, aEvent,
  + aFlags);
  - if (aEvent == AVAHI_BROWSER_FAILURE)
  - {
  - mPublisherAvahi->OnServiceResolveFailed(*this, avahi_client_errno(mPublisherAvahi->mClient));
  - }
  - else
  + switch (aEvent)
  {
  + case AVAHI_BROWSER_NEW:
  Resolve(aInterfaceIndex, aProtocol, aName, aType);
  + break;
  + case AVAHI_BROWSER_REMOVE:
  + // TODO: handle service removing
  + break;
  + case AVAHI_BROWSER_CACHE_EXHAUSTED:
  + case AVAHI_BROWSER_ALL_FOR_NOW:
  + break;
  + case AVAHI_BROWSER_FAILURE:
  + mPublisherAvahi->OnServiceResolveFailed(*this, avahi_client_errno(mPublisherAvahi->mClient));
  + break;
  }
  +
  if (mServiceBrowser != nullptr)
  {
  avahi_service_browser_free(mServiceBrowser);
  