title: PhpSpreadsheet chunk filter read returning empty rows
body: <p>I'm trying to read an XLSX file by chunks. But some of the chunks are empty on the <code>var_dump</code> out put.
  I'm using PHP7.2 and Laravel 5.5 framework.</p>
  
  <p>That is what I've tried so far:</p>
  
  <h2>Filter</h2>
  
  <pre><code>class ChunkReadFilter implements IReadFilter
  {
  private $startRow = 0;
  private $endRow   = 0;
  
  // Set the list of rows that we want to read  
  public function setRows($startRow, $chunkSize) {
      $this-&gt;startRow = $startRow;
      $this-&gt;endRow   = $startRow + $chunkSize;
  }
  
  public function readCell($column, $row, $worksheetName = '') {
      //  Only read the heading row, and the configured rows
    // if (($row == 1) || ($row &gt;= $this-&gt;startRow &amp;&amp; $row &lt; $this-&gt;endRow)) {
   if (($row &gt;= $this-&gt;startRow &amp;&amp; $row &lt; $this-&gt;endRow)) {
          if (in_array($column, range('A', 'L'))) {
              return true;
          }
  
      }
      return false;
  }
  }
  </code></pre>
  
  <h2>Code</h2>
  
  <pre><code>$inputFileType = 'Xlsx';
  $inputFileName = $path;
  
  $reader = IOFactory::createReader($inputFileType);
  $chunkSize = 100;
  $chunkFilter = new ChunkReadFilter();
  for ($startRow = 1; $startRow &lt;= 800; $startRow += $chunkSize) {
  
       //Tell the Read Filter which rows we want this iteration  
      $chunkFilter-&gt;setRows($startRow,$chunkSize);
      //Tell the Reader that we want to use the Read Filter 
      $reader-&gt;setReadFilter($chunkFilter);
      //Load only the rows that match our filter  
      $spreadsheet = $reader-&gt;load($inputFileName);
      //Do some processing here
      $sheetData = $spreadsheet-&gt;getActiveSheet()
     -&gt;toArray(null, true, true, true);
  
        var_dump($sheetData);
     }
  </code></pre>