Symbols are returned with a content length

tests/handlers/api/controller/test_symbol.py

@@ -36,6 +36,7 @@ def test_get(http_controller):
     response = http_controller.get('/symbols/' + urllib.parse.quote(':/symbols/firewall.svg') + '/raw')
     assert response.status == 200
     assert response.headers['CONTENT-TYPE'] == 'image/svg+xml'
+    assert response.headers['CONTENT-LENGTH'] == '9381'
     assert '</svg>' in response.html
 
     # Reply by the default symbol