Preserve config string terminator when preparing key updates

src/config_updater.c

@@ -479,7 +479,7 @@ int config_ensure_keys_and_node_id(const char *filename) {
         buf_capacity = file_size + 1024;
         work_buf = u_malloc(buf_capacity);
         if (!work_buf) { u_free(file_buf); return -1; }
-        memcpy(work_buf, file_buf, file_size);
+        memcpy(work_buf, file_buf, file_size + 1); /* Helpers use strchr; preserve the terminating NUL. */
         work_len = file_size;
         u_free(file_buf); file_buf = NULL;
     }