Gossip outbound stream is not yet opened on heartbeat

20:55:47.258 WARN  - Exception in gossipsub heartbeat
io.libp2p.core.InternalErrorException: Outbound gossip stream not initialized or protocol is missing
        at io.libp2p.pubsub.gossip.GossipRouterKt.getOutboundProtocol(GossipRouter.kt:40) ~[jvm-libp2p-minimal-0.5.8-RELEASE.jar:?]
        at io.libp2p.pubsub.gossip.GossipRouterKt.getOutboundGossipProtocol(GossipRouter.kt:42) ~[jvm-libp2p-minimal-0.5.8-RELEASE.jar:?]
        at io.libp2p.pubsub.gossip.GossipRouter.enqueuePrune(GossipRouter.kt:457) ~[jvm-libp2p-minimal-0.5.8-RELEASE.jar:?]
        at io.libp2p.pubsub.gossip.GossipRouter.prune(GossipRouter.kt:442) ~[jvm-libp2p-minimal-0.5.8-RELEASE.jar:?]
        at io.libp2p.pubsub.gossip.GossipRouter.heartbeat(GossipRouter.kt:371) [jvm-libp2p-minimal-0.5.8-RELEASE.jar:?]

While the WARN log was fixed the stacktrace is suspicious: why gossip outbound stream is not opened on heartbeat? Normally outbound stream can be not yet opened at some moments when gossip initiated by a remote peer and immediately sending some message (see #160). But the outbound stream should be opened immediately and it's unlikely that during heartbeat it's not opened yet.

See the issue comment: https://github.com/ConsenSys/teku/issues/2836#issuecomment-726357019

Start in GossipRouter.kt at heartbeat (line 371), prune (line 442), enqueuePrune (line 457), and the outbound protocol accessors at lines 40 and 42. Trace how the outbound gossip stream is initialized when gossip starts remotely, then determine why heartbeat can reach the missing protocol state. Done means heartbeat no longer produces this exception when the stream has not yet been opened.