SSH: Add missing library initialization.

Botan requires to be initialized before first use. We do that on-demand,
but currently we miss one of the two places where this is necessary.
The problem only manifests itself with multithreading, because Botan
itself also does an on-demand initialization, but does not guard
against concurrent access when doing so.

Task-number: QTCREATORBUG-9980
Change-Id: Id65c428e3d8842c8a6f16942b11d52412239d3c9
Reviewed-by: David Kaspar <dkaspar@blackberry.com>
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>