Fixbug:s-p parent_span_id not found (#19829)

**Phenomenon and reproduction steps**

**Root cause and solution**

**Impactions**

**Test method**

**Affected branch(es)**

* main

**Checklist**

- [ ] Dependencies update required
- [ ] Common bug (similar problem in other repo)

app/app/application/l7_flow_tracing.py

@@ -1322,6 +1322,8 @@ def service_sort(services, app_flows):
 
             server_process_parent_span_id = services[i].direct_flows[0].get(
                 "parent_span_id", None)
+            if server_process_parent_span_id not in app_flows_map:
+                continue
             # s-p没有c-app的parent
             if server_process_parent_span_id is None or server_process_parent_span_id == '':
                 continue