boltdb: fix RangeIterator outside of range seeks

Two issues:
- Seeking before i.start and iterating returned keys before i.start
- Seeking after the store last key did not invalidate the iterator and
  could cause infinite loops.

index/store/boltdb/iterator.go

@@ -29,14 +29,19 @@ type Iterator struct {
 
 func (i *Iterator) updateValid() {
 	i.valid = (i.key != nil)
-	if i.valid && i.prefix != nil {
-		i.valid = bytes.HasPrefix(i.key, i.prefix)
-	} else if i.end != nil {
-		i.valid = bytes.Compare(i.key, i.end) < 0
+	if i.valid {
+		if i.prefix != nil {
+			i.valid = bytes.HasPrefix(i.key, i.prefix)
+		} else if i.end != nil {
+			i.valid = bytes.Compare(i.key, i.end) < 0
+		}
 	}
 }
 
 func (i *Iterator) Seek(k []byte) {
+	if bytes.Compare(k, i.start) < 0 {
+		k = i.start
+	}
 	i.key, i.val = i.cursor.Seek(k)
 	i.updateValid()
 }

index/store/boltdb/store_test.go

@@ -72,6 +72,12 @@ func TestBoltDBRangeIterator(t *testing.T) {
 	test.CommonTestRangeIterator(t, s)
 }
 
+func TestBoltDBRangeIteratorSeek(t *testing.T) {
+	s := open(t, nil)
+	defer cleanup(t, s)
+	test.CommonTestRangeIteratorSeek(t, s)
+}
+
 func TestBoltDBMerge(t *testing.T) {
 	s := open(t, &test.TestMergeCounter{})
 	defer cleanup(t, s)