Branches inspector: fix crash on double click with no selection

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@10638 7b3f36aa-e6db-49c1-8b4c-66eac1997e64
Branches inspector; don't switch branch on double click

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@10639 7b3f36aa-e6db-49c1-8b4c-66eac1997e64