Alternative connections are only attempted if alternative connection data has been configured

Current Situation

If the connection to the source or target fails then a further connection to an alternative source or target is always attempted, although no alternative connection data has been configured.
In particular, the protocol of an alternative connection is not configured so that the following error occurs:

SOSVfs_E_0203: undefined Virtual File System requested

This overwrites the original connection fail message.

Desired Behavior

An alternative connection to a source or target should only be attempted if alternative connection data has been configured.