Fix callback accessing invalid reference to promise (#268)

### Public-Facing Changes

Fix callback accessing invalid reference to promise

### Description
For ROS1, the service request and response types can only be retrieved
by opening a connection to the service server. For this, we use
`ros::ServiceManager::instance()->createServiceServerLink` which under
the hood keeps a copy of the returned pointer, effectively keeping the
connection alive. This patch makes sure that we drop the connection when
we either have received the header or when the timeout has been
exceeded. This avoids that the header-received callback is being called
with an invalid reference to the promise.

Fixes #267 
Resolves FG-5366

ros1_foxglove_bridge/src/service_utils.cpp

@@ -22,18 +22,23 @@ std::string retrieveServiceType(const std::string& serviceName, std::chrono::mil
   auto future = promise.get_future();
 
   link->getConnection()->setHeaderReceivedCallback(
-    [&promise](const ros::ConnectionPtr&, const ros::Header& header) {
+    [&promise](const ros::ConnectionPtr& conn, const ros::Header& header) {
       std::string serviceType;
       if (header.getValue("type", serviceType)) {
         promise.set_value(serviceType);
       } else {
         promise.set_exception(std::make_exception_ptr(
           std::runtime_error("Key 'type' not found in service connection header")));
       }
+      // Close connection since we don't need it any more.
+      conn->drop(ros::Connection::DropReason::Destructing);
       return true;
     });
 
   if (future.wait_for(timeout) != std::future_status::ready) {
+    // Drop connection here, removes the link from the service manager instance and avoids
+    // that the header-received callback is called after the promise has already been destroyed.
+    link->getConnection()->drop(ros::Connection::DropReason::Destructing);
     throw std::runtime_error("Timed out when retrieving service type");
   }