Avoid lost and repeated notifications

Exit without touching the state when checkupdates fails, so a transient
error no longer clears it and causes the same notification on the next
run. Also save the state only after notify-send succeeds, so a failed
notification is retried.

update-notify

@@ -31,8 +31,7 @@ notify_once() {
     if [[ -f $file && $(<"$file") == "$body" ]]; then
         return 0
     fi
-    printf '%s' "$body" > "$file"
-    notify-send "$title" "$body"
+    notify-send "$title" "$body" && printf '%s' "$body" > "$file"
 }
 
 # Forget a key so the next occurrence notifies again.
@@ -75,7 +74,9 @@ latest_version() {
 checkupdates_out=$(checkupdates 2>/dev/null)
 checkupdates_rc=$?
 if (( checkupdates_rc == 1 )); then
+    # Bail out without touching the state, so the next good run doesn't re-notify
     echo "checkupdates failed (network or sync problem?)" >&2
+    exit 1
 fi
 
 arch_list=()