Refactor: for total_token_count method use if to check first. (#9707)

### What problem does this PR solve?

for total_token_count method use if to check first, to improve the
performance when we need to handle exception cases

### Type of change

- [x] Refactoring

rag/llm/rerank_model.py

@@ -44,14 +44,17 @@ class Base(ABC):
         raise NotImplementedError("Please implement encode method!")
 
     def total_token_count(self, resp):
-        try:
-            return resp.usage.total_tokens
-        except Exception:
-            pass
-        try:
-            return resp["usage"]["total_tokens"]
-        except Exception:
-            pass
+        if hasattr(resp, "usage") and hasattr(resp.usage, "total_tokens"):
+            try:
+                return resp.usage.total_tokens
+            except Exception:
+                pass
+
+        if 'usage' in resp and 'total_tokens' in resp['usage']:
+            try:
+                return resp["usage"]["total_tokens"]
+            except Exception:
+                pass
         return 0