Fix HLOOKUP on single row (#1512)

Fixes a bug when doing a HLOOKUP on a single row.

```php
<?php

require 'vendor/autoload.php';

use PhpOffice\PhpSpreadsheet\Spreadsheet;

$spreadsheet = new Spreadsheet();
$sheet = $spreadsheet->getActiveSheet();

/**
 * Single row.
 */
$singleRow = "=HLOOKUP(10, {5, 10, 15}, 1, 0)";
$sheet->getCell('A1')->setValue($singleRow);

// Should echo 10, but echos '#N/A' and some PHP notices and warnings.
echo $sheet->getCell('A1')->getCalculatedValue() . PHP_EOL;

/**
 * Multiple rows.
 */
$multipleRows = "=HLOOKUP(10, {5, 10, 15; 20, 25, 30}, 1, 0)";
$sheet->getCell('A2')->setValue($multipleRows);

// Should echo: 10 and also does.
echo $sheet->getCell('A2')->getCalculatedValue() . PHP_EOL;
```

Co-authored-by: Mark Baker <mark@lange.demon.co.uk>

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 ### Fixed
 
 - Resolve evaluation of utf-8 named ranges in calculation engine [#1522](https://github.com/PHPOffice/PhpSpreadsheet/pull/1522)
+- Fix HLOOKUP on single row [#1512](https://github.com/PHPOffice/PhpSpreadsheet/pull/1512)
 - Fix MATCH when comparing different numeric types [#1521](https://github.com/PHPOffice/PhpSpreadsheet/pull/1521)
 - Fix exact MATCH on ranges with empty cells [#1520](https://github.com/PHPOffice/PhpSpreadsheet/pull/1520)
 

src/PhpSpreadsheet/Calculation/LookupRef.php

@@ -807,7 +807,7 @@ class LookupRef
             return Functions::REF();
         }
         $f = array_keys($lookup_array);
-        $firstRow = array_pop($f);
+        $firstRow = reset($f);
         if ((!is_array($lookup_array[$firstRow])) || ($index_number > count($lookup_array))) {
             return Functions::REF();
         }

tests/data/Calculation/LookupRef/HLOOKUP.php

@@ -275,6 +275,19 @@ return [
         2,
         true,
     ],
+    [
+        3,
+        3,
+        [
+            [
+                1,
+                2,
+                3,
+            ],
+        ],
+        1,
+        true,
+    ],
     [
         5,
         'x',