Fix switching to an empty virtual library not blanking the book details panel

src/calibre/gui2/library/views.py

@@ -763,6 +763,8 @@ class BooksView(QTableView):  # {{{
         idx = self.currentIndex()
         if idx.isValid():
             self._model.current_changed(idx, idx)
+            return True
+        return False
 
     def scrollContentsBy(self, dx, dy):
         # Needed as Qt bug causes headerview to not always update when scrolling

src/calibre/gui2/search_restriction_mixin.py

@@ -587,7 +587,8 @@ class SearchRestrictionMixin(object):
         v = self.current_view()
         if not v.currentIndex().isValid():
             v.set_current_row()
-        v.refresh_book_details()
+        if not v.refresh_book_details():
+            self.book_details.reset_info()
 
     def set_number_of_books_shown(self):
         db = self.library_view.model().db