Finishing evalSpanTimer always before return

Signed-off-by: Alan Protasio <approtas@amazon.com>

promql/engine.go

@@ -653,12 +653,12 @@ func (ng *Engine) execEvalStmt(ctx context.Context, query *query, s *parser.Eval
 		query.sampleStats.InitStepTracking(start, start, 1)
 
 		val, warnings, err := evaluator.Eval(s.Expr)
+		evalSpanTimer.Finish()
+
 		if err != nil {
 			return nil, warnings, err
 		}
 
-		evalSpanTimer.Finish()
-
 		var mat Matrix
 
 		switch result := val.(type) {
@@ -704,10 +704,12 @@ func (ng *Engine) execEvalStmt(ctx context.Context, query *query, s *parser.Eval
 	}
 	query.sampleStats.InitStepTracking(evaluator.startTimestamp, evaluator.endTimestamp, evaluator.interval)
 	val, warnings, err := evaluator.Eval(s.Expr)
+
+	evalSpanTimer.Finish()
+
 	if err != nil {
 		return nil, warnings, err
 	}
-	evalSpanTimer.Finish()
 
 	mat, ok := val.(Matrix)
 	if !ok {