E-book viewer: Clear history when reloading the book, to avoid errors, since the locations pointed to by the history may no longer be valid anyway

src/calibre/gui2/viewer/main.py

@@ -955,6 +955,7 @@ class EbookViewer(MainWindow):
                 reopen_at = self.current_page_bookmark
             except Exception:
                 reopen_at = None
+            self.history.clear()
             self.load_ebook(self.iterator.pathtoebook, reopen_at=reopen_at)
             return
 

src/calibre/gui2/viewer/ui.py

@@ -106,14 +106,15 @@ class History(list):  # {{{
         self.action_back = action_back
         self.action_forward = action_forward
         super(History, self).__init__(self)
+        self.clear()
+
+    def clear(self):
+        del self[:]
         self.insert_pos = 0
         self.back_pos = None
         self.forward_pos = None
         self.set_actions()
 
-    def clear(self):
-        del self[:]
-
     def set_actions(self):
         if self.action_back is not None:
             self.action_back.setDisabled(self.back_pos is None)