core/state/snapshot: be very noisy if the generator hits a trie error (#28178)

core/state/snapshot/generate.go

@@ -446,6 +446,10 @@ func (dl *diskLayer) generateRange(ctx *generatorContext, trieId *trie.ID, prefi
 		internal += time.Since(istart)
 	}
 	if iter.Err != nil {
+		// Trie errors should never happen. Still, in case of a bug, expose the
+		// error here, as the outer code will presume errors are interrupts, not
+		// some deeper issues.
+		log.Error("State snapshotter failed to iterate trie", "err", err)
 		return false, nil, iter.Err
 	}
 	// Delete all stale snapshot states remaining