nixos/…/swap.nix: add some safety assertions for randomEncryption

nixos/modules/config/swap.nix

···
 
         createSwapDevice = sw:
           assert sw.device != "";
+          assert !(sw.randomEncryption && lib.hasPrefix "/dev/disk/by-uuid"  sw.device);
+          assert !(sw.randomEncryption && lib.hasPrefix "/dev/disk/by-label" sw.device);
           let realDevice' = escapeSystemdPath sw.realDevice;
           in nameValuePair "mkswap-${sw.deviceName}"
           { description = "Initialisation of swap device ${sw.device}";