Add corpus analysis fix

app/templates/main/corpora/corpus_analysis.html.j2

@@ -52,6 +52,8 @@
     </form>
       <span class="card-title">Download Results</span>
       <p>Downlaod all results of the current query as csv, excel or json file.</p>
+      <form method="POST">
+        {{ form.hidden_tag() }}
         <div class="input-field">
           <i class="material-icons prefix">insert_drive_file</i>
           {{ dl_form.file_type() }}
@@ -65,6 +67,7 @@
             <i class="material-icons left">file_download</i>
           </button>
         </div>
+      </form>
     </div>
   </div>
 </div>