smb: do not hide enum warnings via switch default label

Summary:
should we ever extend the url types the compiler will not warn us that
the new type may need handling. instead return when we have handled
a type so the fallback can be moved after the switch

Reviewers: ngraham

Reviewed By: ngraham

Subscribers: kde-frameworks-devel, kfm-devel

Tags: #dolphin, #frameworks

Differential Revision: https://phabricator.kde.org/D27644