并发调用文心模型，获取token时出现异常问题修复

第一个请求获取到BaiduAccessToken对象就释放了锁，此时对象中的access_token还是空。第二个请求马上进来直接拿走这个对象，导致获取到的access_token为空，进而导致请求模型报错

api/core/model_runtime/model_providers/wenxin/_common.py

@@ -79,11 +79,13 @@ def get_access_token(api_key: str, secret_key: str) -> 'BaiduAccessToken':
             # if access token not in cache, request it
             token = BaiduAccessToken(api_key)
             baidu_access_tokens[api_key] = token
-            # release it to enhance performance
-            # btw, _get_access_token will raise exception if failed, release lock here to avoid deadlock
-            baidu_access_tokens_lock.release()
-            # try to get access token
-            token_str = BaiduAccessToken._get_access_token(api_key, secret_key)
+            try:
+                # try to get access token
+                token_str = BaiduAccessToken._get_access_token(api_key, secret_key)
+            finally:
+                # release it to enhance performance
+                # btw, _get_access_token will raise exception if failed, release lock here to avoid deadlock
+                baidu_access_tokens_lock.release()
             token.access_token = token_str
             token.expires = now + timedelta(days=3)
             return token