fix(devices): deleting an unpaired MAG or Enigma2 device failed

MagService::getById() and EnigmaService::getById() look up the paired line
with UserRepository::getLineById($rRow['user']['pair_id']), and pair_id is
NULL for a device without a pair. The `int` type the cs-fix pass (758a9cab)
put on getLineById() made that a TypeError, so loading such a device —
deleting it, among others — answered an empty page and changed nothing.
Found by the new E2E device test.

getLineById() is also fed activation codes' nullable subscriber_id and raw
request values, so the guard lives there: anything that is not a positive id
finds nothing, as the untyped version did.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016WDhDajBPziJwjWZcXnh6R

src/Domain/User/UserRepository.php

@@ -425,12 +425,18 @@ class UserRepository {
 	/**
 	 * Fetch a line by id.
 	 *
-	 * @param int $rID Line id.
+	 * @param int|string|null $rID Line id. Callers hand over nullable columns (a
+	 *                             device's `pair_id`) and request values; anything
+	 *                             that is not a positive id finds nothing.
 	 * @return array|null The line row, or null if not found.
 	 */
-	public static function getLineById(int $rID) {
+	public static function getLineById($rID) {
+		if (!is_numeric($rID) || (int) $rID <= 0) {
+			return null;
+		}
+
 		$db = self::db();
-		$db->query('SELECT * FROM `lines` WHERE `id` = ?;', $rID);
+		$db->query('SELECT * FROM `lines` WHERE `id` = ?;', (int) $rID);
 
 		if ($db->num_rows() == 1) {
 			return $db->get_row();

tests/Unit/UserRepositoryTest.php

@@ -111,4 +111,16 @@ final class UserRepositoryTest extends TestCase {
 		// An id-based lookup carries no username/password to re-verify.
 		$this->assertTrue($this->call('verifyCachedCredentials', array(), 5, null, null));
 	}
+
+	/**
+	 * getLineById() is handed nullable columns (a MAG / Enigma2 device's
+	 * `pair_id`, an activation code's `subscriber_id`) and raw request values.
+	 * None of those is a line, and none may end the request: loading an
+	 * unpaired MAG device used to throw, so deleting one answered an empty page.
+	 */
+	public function testGetLineByIdFindsNothingForANonId(): void {
+		foreach (array(null, '', 0, '0', -3, 'abc') as $rID) {
+			$this->assertNull(UserRepository::getLineById($rID), var_export($rID, true));
+		}
+	}
 }