use copy bytes to avoid side effect

Author: hadv

kvdb/flushable/flushable.go

@@ -78,7 +78,7 @@ func (w *Flushable) Put(key []byte, value []byte) error {
 }
 
 func (w *Flushable) put(key []byte, value []byte) {
-	w.modified.Put(key, common.CopyBytes(value))
+	w.modified.Put(common.CopyBytes(key), common.CopyBytes(value))
 	*w.sizeEstimation += len(key) + len(value) + 128
 }
 
@@ -128,7 +128,7 @@ func (w *Flushable) Delete(key []byte) error {
 }
 
 func (w *Flushable) delete(key []byte) {
-	w.modified.Put(key, nil)
+	w.modified.Put(common.CopyBytes(key), nil)
 	*w.sizeEstimation += len(key) + 128 // it should be (len(key) - len(old value)), but we'd need to read old value
 }