Options: add filter is none assert

Signed-off-by: Cholerae Hu <huyingqian@pingcap.com>

src/rocksdb_options.rs

@@ -320,8 +320,8 @@ impl Default for Options {
 }
 
 impl Clone for Options {
-    // Only copy DBOptions.
     fn clone(&self) -> Self {
+        assert!(self.filter.is_none());
         unsafe {
             let opts = crocksdb_ffi::crocksdb_options_copy(self.inner);
             assert!(!opts.is_null());