fix:storage:avoid panic when iterater exhauested (#9945)

Signed-off-by: detailyang <detailyang@gmail.com>

storage/buffer.go

@@ -82,7 +82,7 @@ func (b *BufferedSeriesIterator) Seek(t int64) bool {
 
 	// If the delta would cause us to seek backwards, preserve the buffer
 	// and just continue regular advancement while filling the buffer on the way.
-	if t0 > b.lastTime {
+	if b.ok && t0 > b.lastTime {
 		b.buf.reset()
 
 		b.ok = b.it.Seek(t0)

storage/buffer_test.go

@@ -149,6 +149,7 @@ func TestBufferedSeriesIterator(t *testing.T) {
 	bufferEq([]sample{{t: 99, v: 8}, {t: 100, v: 9}})
 
 	require.False(t, it.Next(), "next succeeded unexpectedly")
+	require.False(t, it.Seek(1024), "seek succeeded unexpectedly")
 }
 
 // At() should not be called once Next() returns false.

storage/memoized_iterator.go

@@ -71,7 +71,7 @@ func (b *MemoizedSeriesIterator) PeekPrev() (t int64, v float64, ok bool) {
 func (b *MemoizedSeriesIterator) Seek(t int64) bool {
 	t0 := t - b.delta
 
-	if t0 > b.lastTime {
+	if b.ok && t0 > b.lastTime {
 		// Reset the previously stored element because the seek advanced
 		// more than the delta.
 		b.prevTime = math.MinInt64

storage/memoized_iterator_test.go

@@ -68,6 +68,7 @@ func TestMemoizedSeriesIterator(t *testing.T) {
 	prevSampleEq(100, 9, true)
 
 	require.False(t, it.Next(), "next succeeded unexpectedly")
+	require.False(t, it.Seek(1024), "seek succeeded unexpectedly")
 }
 
 func BenchmarkMemoizedSeriesIterator(b *testing.B) {