A bounded LoopProcessLogData (stopTsNs set) on a buffer that never took a
write since process start fell into the ResumeFromDiskError branch, which
never checks stopTsNs when ReadFromDiskFn is nil and HasData() is false.
The read parked on the notification loop forever while the subscription's
idle heartbeats kept the stream looking alive, so a bounded
SubscribeMetadata pass on a freshly restarted idle filer never completed.
Terminate like the caught-up path does, returning a nil error: leaking
the pending ResumeFromDiskError would latch the filer's outer loop into
its gap machinery, which parks the bounded subscriber all over again.