New option --wapp-url never raise the correct error

[Qwarctick]

Description

With #554

An error when downloading the database should print an error message Error downloading wapp database. https://github.com/OussamaBeng/wapiti/blob/master/wapitiCore/attack/mod_wapp.py#L121

Instead, there is juste a Non-200 status code and a message Update done (which is wrong).

Steps to reproduce

$ wapiti --update -m wapp --wapp-url "https://foobar123.com"
Wapiti 3.1.8 (wapiti-scanner.github.io)
[*] Updating modules
Updating module wapp
Error: Non-200 status code for _.json. Skipping.
Update done.
$ echo $?
0

[bretfourbe]

Fixed by #562