fix: handle namespaced helper found on Common helper

Author: samsonasik

system/Common.php

@@ -598,7 +598,7 @@ function helper($filenames): void
             if (str_contains($filename, '\\')) {
                 $path = $loader->locateFile($filename, 'Helpers');
 
-                if ($path !== '') {
+                if ($path === false) {
                     throw FileNotFoundException::forFileNotFound($filename);
                 }
 

tests/system/CommonHelperTest.php

@@ -13,7 +13,9 @@
 
 namespace CodeIgniter;
 
+use CodeIgniter\Autoloader\Autoloader;
 use CodeIgniter\Autoloader\FileLocator;
+use CodeIgniter\Files\Exceptions\FileNotFoundException;
 use CodeIgniter\Test\CIUnitTestCase;
 use Config\Services;
 use PHPUnit\Framework\Attributes\CoversFunction;
@@ -148,4 +150,25 @@ function foo_bar_baz(): string
 
         $this->assertSame($this->dummyHelpers[0], foo_bar_baz());
     }
+
+    public function testNamespacedHelperNotFound(): void
+    {
+        $this->expectException(FileNotFoundException::class);
+
+        $locator = $this->getMockLocator();
+        Services::injectMock('locator', $locator);
+
+        helper('foo\barbaz');
+    }
+
+    public function testNamespacedHelperFound(): void
+    {
+        $autoloader = new Autoloader();
+        $autoloader->addNamespace('Tests\Support\Helpers', TESTPATH . '_support/Helpers');
+        $locator = new FileLocator($autoloader);
+
+        Services::injectMock('locator', $locator);
+
+        helper('Tests\Support\Helpers\baguette');
+    }
 }