Merge pull request #218956 from lourkeur/slstatus

slstatus: fix overriden build

pkgs/applications/misc/slstatus/default.nix

···
   };
 
   configFile = lib.optionalString (conf!=null) (writeText "config.def.h" conf);
-  preBuild = lib.optionalString (conf!=null) "cp ${configFile} config.def.h" + ''
+  preBuild = ''
+    ${lib.optionalString (conf!=null) "cp ${configFile} config.def.h"}
     makeFlagsArray+=(LDLIBS="-lX11 -lxcb -lXau -lXdmcp" CC=$CC)
   '';