update sift to match docstring (#245)

Closes #244.

Reviewed-on: #245
Reviewed-by: James Mills <james@mills.io>
Co-authored-by: Tai Groot <tai@taigrr.com>
Co-committed-by: Tai Groot <tai@taigrr.com>

bitcask.go

@@ -264,7 +264,9 @@ func (b *Bitcask) Sift(f func(key []byte) (bool, error)) (err error) {
 		return true
 	})
 	b.mu.RUnlock()
-
+	if err != nil {
+		return
+	}
 	b.mu.Lock()
 	defer b.mu.Unlock()
 	keysToDelete.ForEach(func(node art.Node) (cont bool) {
@@ -343,6 +345,10 @@ func (b *Bitcask) SiftScan(prefix []byte, f func(key []byte) (bool, error)) (err
 	})
 	b.mu.RUnlock()
 
+	if err != nil {
+		return
+	}
+
 	b.mu.Lock()
 	defer b.mu.Unlock()
 	keysToDelete.ForEach(func(node art.Node) (cont bool) {
@@ -422,6 +428,10 @@ func (b *Bitcask) SiftRange(start, end []byte, f func(key []byte) (bool, error))
 	})
 	b.mu.RUnlock()
 
+	if err != nil {
+		return
+	}
+
 	b.mu.Lock()
 	defer b.mu.Unlock()