Fixing nil safe issue

Author: igomeow

modules/exploits/windows/http/pgadmin_binary_path_api.rb

@@ -102,7 +102,7 @@ def get_version
       res = send_request_cgi('uri' => normalize_uri(target_uri.path, 'browser/'), 'keep_cookies' => true)
     end
     html_document = res.get_html_document
-    return unless html_document.xpath('//title').text == 'pgAdmin 4'
+    return unless html_document && html_document.xpath('//title').text == 'pgAdmin 4'
 
     # there's multiple links in the HTML that expose the version number in the [X]XYYZZ,
     # see: https://github.com/pgadmin-org/pgadmin4/blob/053b1e3d693db987d1c947e1cb34daf842e387b7/web/version.py#L27