remotes: test for existance before delete.

Test if the remote exists before deleting it. This guards against two potential issues:
1. A Flatpakref might install non-enumerable remotes that are automatically deleted
   when the application is uninstalled, so attempting to delete them without checking
   could cause errors.
2. Users might manually delete apps/remotes, which could impact nix-flatpak state;
   checking prevents errors if the remote has already been removed.

modules/remotes.nix

@@ -16,13 +16,23 @@ let
     # Delete all remotes that are present in the old state but not the new one
     # $OLD_STATE and $NEW_STATE are globals, declared in the output of pkgs.writeShellScript.
     # If uninstallUnmanagedState is true, then the remotes will be deleted forcefully.
+    #
+    # Test if the remote exists before deleting it. This guards against two potential issues:
+    # 1. A Flatpakref might install non-enumerable remotes that are automatically deleted
+    #    when the application is uninstalled, so attempting to delete them without checking
+    #    could cause errors.
+    # 2. Users might manually delete apps/remotes, which could impact nix-flatpak state;
+    #    checking prevents errors if the remote has already been removed.
     ${pkgs.jq}/bin/jq -r -n \
       --argjson old "$OLD_STATE" \
       --argjson new "$NEW_STATE" \
        '(($old.remotes // []) - ($new.remotes // []))[]' \
       | while read -r REMOTE_NAME; do
-          ${pkgs.flatpak}/bin/flatpak remote-delete ${if uninstallUnmanaged then " --force " else " " } --${installation} $REMOTE_NAME
-
+          if ${pkgs.flatpak}/bin/flatpak --${installation} remotes --columns=name | grep -q "^$REMOTE_NAME$"; then
+            ${pkgs.flatpak}/bin/flatpak remote-delete ${if uninstallUnmanaged then " --force " else " " } --${installation} $REMOTE_NAME
+          else
+            echo "Remote '$REMOTE_NAME' not found in flatpak remotes"
+          fi
       done
   '';