message: Fix exception in integration test if no system is available
diff: @@ -19,6 +19,7 @@ TEST(HardwareTest, LogFiles)
  std::this_thread::sleep_for(std::chrono::seconds(2));
  + ASSERT_EQ(mavsdk.systems().size(), 1);
  auto system = mavsdk.systems().at(0);
  ASSERT_TRUE(system->has_autopilot());
  auto log_files = std::make_shared<LogFiles>(system);
  @@ -72,6 +73,7 @@ TEST(HardwareTest, LogFilesDownloadFailsIfPathIsDirectory)
  std::this_thread::sleep_for(std::chrono::seconds(2));
  + ASSERT_EQ(mavsdk.systems().size(), 1);
  auto system = mavsdk.systems().at(0);
  ASSERT_TRUE(system->has_autopilot());
  auto log_files = std::make_shared<LogFiles>(system);
  @@ -126,6 +128,7 @@ TEST(HardwareTest, LogFilesDownloadFailsIfFileAlreadyExists)
  std::this_thread::sleep_for(std::chrono::seconds(2));
  + ASSERT_EQ(mavsdk.systems().size(), 1);
  auto system = mavsdk.systems().at(0);
  ASSERT_TRUE(system->has_autopilot());
  auto log_files = std::make_shared<LogFiles>(system);
  