fix coverity bug

src/lib/oblog/ob_log.cpp

@@ -1528,12 +1528,15 @@ void ObLogger::do_async_flush_to_file(ObLogItem **log_item, const int64_t count)
         }
       }
 
-      struct iovec vec[MAX_FD_FILE][GROUP_COMMIT_MAX_ITEM_COUNT] = {0};
+      struct iovec vec[MAX_FD_FILE][GROUP_COMMIT_MAX_ITEM_COUNT];
       int iovcnt[MAX_FD_FILE] = {0};
       int large_iovcnt[MAX_FD_FILE] = {0};
-      struct iovec wf_vec[MAX_FD_FILE][GROUP_COMMIT_MAX_ITEM_COUNT] = {0};
+      struct iovec wf_vec[MAX_FD_FILE][GROUP_COMMIT_MAX_ITEM_COUNT];
       int wf_iovcnt[MAX_FD_FILE] = {0};
 
+      memset(vec, 0, sizeof(vec));
+      memset(wf_vec, 0, sizeof(wf_vec));
+
       ObLogFDType fd_type = MAX_FD_FILE;
       for (int64_t i = 0; i < count; ++i) {
         if (OB_ISNULL(log_item[i])) {