Fix calibre startup crash caused by Quickview when the applied virtual library is empty (has no books).

src/calibre/gui2/dialogs/quickview.py

@@ -356,6 +356,7 @@ class Quickview(QDialog, Ui_Quickview):
         if self.lock_qv.isChecked():
             return
 
+        try:
             bv_row = idx.row()
             self.current_column = idx.column()
             key = self.view.column_map[self.current_column]
@@ -363,6 +364,8 @@ class Quickview(QDialog, Ui_Quickview):
             if self.current_book_id == book_id and self.current_key == key:
                 return
             self._refresh(book_id, key)
+        except:
+            self.indicate_no_items()
 
     def _refresh(self, book_id, key):
         '''