Fix selection when inserting multiple items into wxSelectionStore

When inserting more than one item into wxSelectionStore in the
default-selected state, the state of all the items bug the first one was
wrongly set to "selected" initially.

Just fix the typo in the AddAt() call, which was passed a wrong
variable, to fix this.

Closes #19040.

src/generic/selstore.cpp

@@ -207,7 +207,7 @@ void wxSelectionStore::OnItemsInserted(unsigned item, unsigned numItems)
         // items indices.
         for ( unsigned n = item; n < item + numItems; n++ )
         {
-            m_itemsSel.AddAt(item, idx++);
+            m_itemsSel.AddAt(n, idx++);
         }
     }