Handle state when uploading a virus

[mpivchev]

On Android this already works, but for iOS:

Uploading a file with virus should result in a proper error message by server, which then can be handled by clients.

This is how we do it on Android:

• we receive a HTTP 400 Bad Request or HTTP 415 Unsupported Media Type
• we parse the XML error and handle it

https://github.com/nextcloud/android-library/blob/de96ce2bef33512232b41047656e4213542e0e1a/library/src/androidTest/java/com/owncloud/android/ExceptionParserIT.java#L48