fix(streaming): handle missing cache_policy field in OverWindow (#12110)

Author: kwannoel

src/stream/src/from_proto/over_window.rs

@@ -75,7 +75,9 @@ impl ExecutorBuilder for OverWindowExecutorBuilder {
             watermark_epoch: stream.get_watermark_epoch(),
             metrics: params.executor_stats,
             chunk_size: params.env.config().developer.chunk_size,
-            cache_policy: OverWindowCachePolicy::from_protobuf(node.get_cache_policy()?),
+            cache_policy: OverWindowCachePolicy::from_protobuf(
+                node.get_cache_policy().unwrap_or_default(),
+            ),
         })
         .boxed())
     }