buildx/store/storeutil
Milas Bowman 14f5d490ef builder: extra init error handling
* Return errors from creating the `NodeGroup`
* Ensure that `b.NodeGroup != nil` before reading from
  it during validation

Signed-off-by: Milas Bowman <milas.bowman@docker.com>
..
storeutil.go builder: extra init error handling