Fix too long context issue. (#4735)

### What problem does this PR solve?

#4728

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

graphrag/general/community_reports_extractor.py

@@ -70,6 +70,8 @@ class CommunityReportsExtractor(Extractor):
                 weight = ents["weight"]
                 ents = ents["nodes"]
                 ent_df = pd.DataFrame(self._get_entity_(ents)).dropna()#[{"entity": n, **graph.nodes[n]} for n in ents])
+                if ent_df.empty:
+                    continue
                 ent_df["entity"] = ent_df["entity_name"]
                 del ent_df["entity_name"]
                 rela_df = pd.DataFrame(self._get_relation_(list(ent_df["entity"]), list(ent_df["entity"]), 10000))