Fix misuse of isSectionIndex() in visible_columns. isSectionIndex() takes a logical index but a visual index was being given. The misuse led to the problem reported in

https://www.mobileread.com/forums/showthread.php?t=367195

src/calibre/gui2/library/views.py

@@ -1237,9 +1237,7 @@ class BooksView(TableView):  # {{{
     @property
     def visible_columns(self):
         h = self.horizontalHeader()
-        logical_indices = (x for x in range(h.count()) if not h.isSectionHidden(x))
-        rmap = dict(enumerate(self.column_map))
-        return (rmap[h.visualIndex(x)] for x in logical_indices if h.visualIndex(x) > -1)
+        return (key for lidx,key in enumerate(self.column_map) if not h.isSectionHidden(lidx))
 
     def refresh_book_details(self, force=False):
         idx = self.currentIndex()