MetaReader Update, 22.0 branch (2022.09.20.)
This is a sibling of !56727 (merged). Apparently during Partial Event Building the run number information may also be missing from the ByteStream metadata.
So now the code takes the run number of the first event if the BS metadata didn't contain anything usable. Much like what !56727 (merged) did for the lumiblock information.
As !56727 (merged), this is also in an effort to help with ATLASRECTS-7126.