Fix numerous PHP 8.1 "strlen(null)" exceptions which block rendering the Applications page

Summary:
`strlen()` was used in Phabricator to check if a generic value is a non-empty string.
This behavior is deprecated since PHP 8.1. Phorge adopts `phutil_nonempty_string()` as a replacement.

Note: this may highlight other absurd input values that might be worth correcting
instead of just ignoring. If phutil_nonempty_string() throws an exception in your
instance, report it to Phorge to evaluate and fix that specific corner case.

Closes T15294

Test Plan: Applied these three changes and `/applications/` finally rendered in web browser.

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15294

Differential Revision: https://we.phorge.it/D25144

src/applications/meta/query/PhabricatorAppSearchEngine.php

@@ -45,7 +45,7 @@ final class PhabricatorAppSearchEngine
       ->withUnlisted(false);
 
     $name = $saved->getParameter('name');
-    if (strlen($name)) {
+    if (phutil_nonempty_string($name)) {
       $query->withNameContains($name);
     }
 

src/applications/search/controller/PhabricatorApplicationSearchController.php

@@ -115,7 +115,7 @@ final class PhabricatorApplicationSearchController
     if ($this->queryKey == 'advanced') {
       $run_query = false;
       $query_key = $request->getStr('query');
-    } else if (!strlen($this->queryKey)) {
+    } else if (!phutil_nonempty_string($this->queryKey)) {
       $found_query_data = false;
 
       if ($request->isHTTPGet() || $request->isQuicksand()) {

src/view/layout/AphrontSideNavFilterView.php

@@ -145,7 +145,7 @@ final class AphrontSideNavFilterView extends AphrontView {
 
   public function selectFilter($key, $default = null) {
     $this->selectedFilter = $default;
-    if ($this->menu->getItem($key) && strlen($key)) {
+    if ($this->menu->getItem($key) && phutil_nonempty_string($key)) {
       $this->selectedFilter = $key;
     }
     return $this->selectedFilter;