[EDH-3706] Error when sending Joint invoice "Grid agreement not found"

[mailimarkvardt]

Problem
In some cases joint invoices cannot be sent due to seemingly missing grid agreement, although the grid agreement exists and is valid.
Does not happen with all metering points, pattern unknown at the moment.

Steps to reproduce

1. choose GO and OS pair that has valid joint invoice agreement
2. from metering points owned by this GO, choose a metering point that has valid GRID agreement
3. Create joint invoice

Expected result
Successfully added joint invoice

Actual result
"Grid agreement not found" error message