Fix RepositorySearchDialog when browsing different directories

When clicking "Browse" multiple times for different directories
containing repositories the RepositorySearchDialog only displayed the
repositories selected in the last browse step but also added
repositories selected in earlier browse steps. This is surprising as the
latter weren't displayed before finishing the wizard.

Bug: 450213
Change-Id: I6081f933000b6f92c73ac7817d625b0472ca1f2f
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>