fix(pruner): fix find algo so that it does not pass a malformed range…

… into `GetRangeByHeight` call (#3828)

pruner/find.go

@@ -31,15 +31,17 @@ func (s *Service) findPruneableHeaders(
 		return nil, err
 	}
 
-	if lastPruned.Height() == estimatedCutoffHeight {
+	if lastPruned.Height() >= estimatedCutoffHeight {
 		// nothing left to prune
 		return nil, nil
 	}
 
 	log.Debugw("finder: fetching header range", "last pruned", lastPruned.Height(),
 		"target height", estimatedCutoffHeight)
 
-	headers, err := s.getter.GetRangeByHeight(ctx, lastPruned, estimatedCutoffHeight)
+	// GetRangeByHeight requests (from:to), where `to` is non-inclusive, we need
+	// to request one more header than the estimated cutoff
+	headers, err := s.getter.GetRangeByHeight(ctx, lastPruned, estimatedCutoffHeight+1)
 	if err != nil {
 		log.Errorw("failed to get range from header store", "from", lastPruned.Height(),
 			"to", estimatedCutoffHeight, "error", err)