SUPPORT-9333. fix multipart payload parsing

src/utils/detached_sign_payload_parser.c

@@ -118,7 +118,7 @@ on_header_value(multipart_parser* parser, const char *at, size_t length)
         if (check_content_type(&data->content_type)) {
             goto error;
         }
-    } else {
+    } else if (data->cur_header != NULL) {
         LOG_ERROR("Unknown header value: '%.*s'", (int) length, at);
         goto error;
     }