[FIXUP] Append unread news items

It's always guaranteed that unread news items from 'newsUnreadIdsFile'
are not already present in 'newsUnreadIdsFile'. Thanks @nonsequitur!

home-manager/home-manager

@@ -194,14 +194,11 @@ function doShowNews() {
             return 1
     esac
 
+    if [[ -s "$newsUnreadIdsFile" ]]; then
         local newsReadIdsFile
         newsReadIdsFile="$(newsReadIdsFile)"
-
-    local tempNewReadIdsFile
-    tempNewReadIdsFile="$(mktemp -t hm-news-read-ids.XXXXXXXXXX)"
-
-    sort -u "$newsReadIdsFile" "$newsUnreadIdsFile" > "$tempNewReadIdsFile"
-    mv -f "$tempNewReadIdsFile" "$newsReadIdsFile"
+        cat "$newsUnreadIdsFile" >> "$newsReadIdsFile"
+    fi
 }
 
 function doHelp() {

home-manager/home-manager.nix

@@ -61,8 +61,13 @@ let
     ) env.newsEntries
   );
 
+  # File where each line corresponds to an unread news entry
+  # identifier. If non-empty then the file ends in "\n".
   newsUnreadIdsFile = pkgs.writeText "news-unread-ids" (
-    concatMapStringsSep "\n" (entry: entry.id) newsFiltered
+    let
+      text = concatMapStringsSep "\n" (entry: entry.id) newsFiltered;
+    in
+      text + optionalString (text != "") "\n"
   );
 
   newsInfo = pkgs.writeText "news-info.sh" ''