[libcalamaresui] Fix isAtVeryEnd()

- With an empty list, the question is meaningless
- .. and we called this with an empty list while constructing the
  ViewManager; if quit-at-end is true, then this would terminate
  Calamares immediately because the list was at the end.

src/libcalamaresui/ViewManager.cpp

@@ -272,8 +272,13 @@ stepIsExecute( const ViewStepList& steps, int index )
 
 static inline bool
 isAtVeryEnd( const ViewStepList& steps, int index )
-
 {
+    // If we have an empty list, then there's no point right now
+    // in checking if we're at the end.
+    if ( steps.count() == 0 )
+    {
+        return false;
+    }
     return ( index >= steps.count() ) || ( index == steps.count() - 1 && steps.last()->isAtEnd() );
 }