Avoid possible infinite recursion

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

hosts/common/user/configs/gui/qalculate/default.nix

@@ -1,5 +1,5 @@
 {
-  user ? throw "user argument is required",
+  username ? throw "username argument is required",
 }:
 {
   lib,
@@ -8,16 +8,17 @@
   ...
 }:
 let
-  hmConfig = config.home-manager.users.${user.name};
+  userConfig = config.users.users.${username};
+  hmConfig = config.home-manager.users.${username};
   qalculate-gtk = pkgs.qalculate-gtk.overrideAttrs (oldAttrs: {
     patches = oldAttrs.patches or [ ] ++ [ ./skip-save-prefs.patch ];
   });
 in
 {
-  home-manager.users.${user.name} = {
+  home-manager.users.${username} = {
     home = {
       packages = [ qalculate-gtk ];
-      persistence."/cache${user.home}".files = [
+      persistence."/cache${userConfig.home}".files = [
         "${hmConfig.xdg.relativeConfigHome}/qalculate/qalculate-gtk.history"
       ];
     };