fix: make sure the memory subsystem is available before accessing the…

… memory limit (#10098) (#10099)

(cherry picked from commit ccda834)

Co-authored-by: kruskall <99559985+kruskall@users.noreply.github.com>

internal/beater/memlimit_cgroup.go

@@ -55,12 +55,18 @@ func cgroupMemoryLimit(rdr *cgroup.Reader) (uint64, error) {
 		if err != nil {
 			return 0, fmt.Errorf("unable to read cgroup limits: %w", err)
 		}
+		if stats.Memory == nil {
+			return 0, fmt.Errorf("cgroup memory subsystem unavailable")
+		}
 		return stats.Memory.Mem.Limit.Bytes, nil
 	case cgroup.CgroupsV2:
 		stats, err := rdr.GetV2StatsForProcess(pid)
 		if err != nil {
 			return 0, fmt.Errorf("unable to read cgroup limits: %w", err)
 		}
+		if stats.Memory == nil {
+			return 0, fmt.Errorf("cgroup memory subsystem unavailable")
+		}
 		return stats.Memory.Mem.Max.Bytes.ValueOr(0), nil
 	}
 	return 0, errors.New("unsupported cgroup version")