Refactor template empty checks (#28351) (#28354)

Backport #28351 by @KN4CK3R

Fix #28347

As there is no info how to reproduce it, I can't test it.
Fix may be `section_split.tmpl @ 126/130`.

Other changes are "empty check" refactorings.

Co-authored-by: KN4CK3R <admin@oldschoolhack.me>

templates/user/notification/notification_subscriptions.tmpl

@@ -63,7 +63,7 @@
 					</div>
 				</div>
 				<div class="divider"></div>
-				{{if eq (len .Issues) 0}}
+				{{if not .Issues}}
 					{{ctx.Locale.Tr "notification.no_subscriptions"}}
 				{{else}}
 					{{template "shared/issuelist" dict "." . "listType" "dashboard"}}