title: Uploading files with codeigniter (3.1) fails
body: <p><br>
  I'm having a problem with uploading files with Codeigniter framework. 
  Currently is working like this:<br>
  If i don't select any file in HTML form, then variables like <code>$title = $this-&gt;input-&gt;post('title');</code> gets value,<br>
  but when i select file in html form, then all variables are null and i get message file is not selected.</p>
  
  <p>My .htaccess file</p>
  
  <pre><code>RewriteEngine On
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteCond %{REQUEST_FILENAME} !-d
  RewriteRule ^(.*)$ index.php/$1 [L]
  </code></pre>
  
  <p>My autoload.php file</p>
  
  <pre><code>$autoload['helper'] = array('url', 'file', 'form');
  $autoload['libraries'] = array('database', 'session', 'email', 'form_validation');
  $autoload['model'] = array('model_services' =&gt; 'ms', 'Model_categories' =&gt; 'mc');
  </code></pre>
  
  <p>My controller which is rendering view:</p>
  
  <pre><code> public function add_catalog() {
          if ($this-&gt;is_admin() == TRUE) {
              $data['cat'] = $this-&gt;mc-&gt;get();
              $this-&gt;load-&gt;view('admin_view_map/admin_header');
              $this-&gt;load-&gt;view('admin_view_map/admin_add_catalog', $data);
              $this-&gt;load-&gt;view('admin_view_map/admin_footer');
          } else {
              $this-&gt;index();
          }
      }
  </code></pre>
  
  <p>HTML:</p>
  
  <pre><code>&lt;?php echo form_open_multipart('admin321/insert_catalog'); ?&gt;
      *title: &lt;input type="text" name="title" /&gt;
      sub_title: &lt;input type="text" name="sub_title" /&gt;
      Facebook url: &lt;input type="text" name="facebookUrl" /&gt;
      Twitter url: &lt;input type="text" name="twitterUrl" /&gt;
      Google +: &lt;input type="text" name="googlePlus" /&gt;
      description: &lt;input type="text" name="description" /&gt;
      pdf: &lt;/span&gt; &lt;input type="file" name="pdf" /&gt;
      categories:
      &lt;select name="categories" &gt;
          &lt;?php foreach ($cat as $r) {
                  echo '&lt;option value=' . $r-&gt;id_category . ' &gt;' . $r-&gt;category . '&lt;/option&gt;';
          } ?&gt;
      &lt;/select&gt;
      &lt;input type="submit" value="Add" class="submit"&gt;
  &lt;?php echo form_close(); ?&gt;
  </code></pre>
  
  <p>PHP:</p>
  
  <pre><code>public function insert_catalog(){
      $title = $this-&gt;input-&gt;post('title');
      $sub_title = $this-&gt;input-&gt;post('sub_title');
      $facebookUrl = $this-&gt;input-&gt;post('facebookUrl');
      $twitterUrl = $this-&gt;input-&gt;post('twitterUrl');
      $googlePlus = $this-&gt;input-&gt;post('googlePlus');
      $description = $this-&gt;input-&gt;post('description');
      $category = $this-&gt;input-&gt;post('categories');
      var_dump($title,$sub_title,$facebookUrl,$twitterUrl,$googlePlus,$description,$category);
  
      $config['upload_path'] = './assets/pdf/';
      $config['allowed_types'] = 'pdf';
      $this-&gt;load-&gt;library('upload', $config);
  
      if (!$this-&gt;upload-&gt;do_upload('pdf')){
          var_dump($this-&gt;upload-&gt;display_errors());
          die();
      }else{
          $pdf = array('upload_data' =&gt; $this-&gt;upload-&gt;data());
          var_dump($pdf);
          die();
      }
  
  }
  </code></pre>
  
  <p>This make result like this:</p>
  
  <pre><code>null
  null
  null
  null
  null
  null
  null
  string '&lt;p&gt;You did not select a file to upload.&lt;/p&gt;' (length=43)
  </code></pre>
  
  <p>I'm using WAMP server and this are my php.ini configuration</p>
  
  <pre><code>; Whether to allow HTTP file uploads.
  ; http://php.net/file-uploads
  file_uploads = On
  
  ; Temporary directory for HTTP uploaded files (will use system default if not
  ; specified).
  ; http://php.net/upload-tmp-dir
  upload_tmp_dir = "e:/wamp/tmp"
  
  ; Maximum allowed size for uploaded files.
  ; http://php.net/upload-max-filesize
  upload_max_filesize = 64M
  </code></pre>