gimbal: fix one based gimbal_id

The gimbal_id is one based because 0 means "all gimbals".

src/mavsdk/plugins/gimbal/gimbal_impl.cpp

@@ -200,8 +200,9 @@ void GimbalImpl::process_gimbal_manager_status(const mavlink_message_t& message)
     auto& gimbal = *maybe_gimbal;
 
     // We need to populate the MAVSDK gimbal ID, so the user knows which is which.
+    // +1 because 0 means all, so it's one-based.
     gimbal.control_status.gimbal_id =
-        static_cast<int32_t>(std::distance(_gimbals.begin(), maybe_gimbal));
+        static_cast<int32_t>(std::distance(_gimbals.begin(), maybe_gimbal)) + 1;
 
     if (status.primary_control_sysid == static_cast<int>(_system_impl->get_own_system_id()) &&
         status.primary_control_compid == static_cast<int>(_system_impl->get_own_component_id())) {
@@ -315,7 +316,9 @@ void GimbalImpl::process_gimbal_device_attitude_status(const mavlink_message_t&
     // Reset to defaults (e.g. NaN) first.
     gimbal.attitude = {};
     // We need to populate the MAVSDK gimbal ID, so the user knows which is which.
-    gimbal.attitude.gimbal_id = static_cast<int32_t>(std::distance(_gimbals.begin(), maybe_gimbal));
+    // +1 because 0 means all, so it's one-based.
+    gimbal.attitude.gimbal_id =
+        static_cast<int32_t>(std::distance(_gimbals.begin(), maybe_gimbal)) + 1;
 
     if (is_in_forward_frame) {
         gimbal.attitude.quaternion_forward.w = attitude_status.q[0];