ubsan: Don’t call v[0] on empty vectors

util/mach/child_port_handshake.cc

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 301 matching lines @@
                                                     std::string* service_name) {
   // Read the token from the pipe.
   CheckedReadFile(pipe_read, token, sizeof(*token));
 
   // Read the service name from the pipe.
   uint32_t service_name_length;
   CheckedReadFile(pipe_read, &service_name_length, sizeof(service_name_length));
   DCHECK_LT(service_name_length,
             implicit_cast<uint32_t>(BOOTSTRAP_MAX_NAME_LEN));
 
-  if (service_name_length > 0) {
-    service_name->resize(service_name_length);
+  service_name->resize(service_name_length);
+  if (!service_name->empty()) {
     CheckedReadFile(pipe_read, &(*service_name)[0], service_name_length);
   }
 }
 
 // static
 void ChildPortHandshake::RunClientInternal_SendCheckIn(
     const std::string& service_name,
     child_port_token_t token,
     mach_port_t port,
     mach_msg_type_name_t right_type) {
   // Get a send right to the server by looking up the service with the bootstrap
   // server by name.
   mach_port_t server_port;
   kern_return_t kr =
       bootstrap_look_up(bootstrap_port, service_name.c_str(), &server_port);
   BOOTSTRAP_CHECK(kr == BOOTSTRAP_SUCCESS, kr) << "bootstrap_look_up";
   base::mac::ScopedMachSendRight server_port_owner(server_port);
 
   // Check in with the server.
   kr = child_port_check_in(server_port, token, port, right_type);
   MACH_CHECK(kr == KERN_SUCCESS, kr) << "child_port_check_in";
 }
 
 }  // namespace crashpad