Handle the case when pdfviewer is asked to go to a page while the file is still loading

Author: jmoraleda

wx/lib/pdfviewer/viewer.py

@@ -292,13 +292,19 @@ def GoPage(self, pagenum):
         :param integer `pagenum`: go to the provided page number if it is valid
 
         """
+        # calling Scroll sometimes doesn't raise wx.EVT_SCROLLWIN eg Windows 8 64 bit - so
+        wx.CallAfter(self.Render)
+
+        if not hasattr(self, "cumYpagespixels"):
+            return False # This could happen if the file is still loading
+        
         if pagenum > 0 and pagenum <= self.numpages:
             self.Scroll(0, self.cumYpagespixels[pagenum-1] //
                            self.GetScrollPixelsPerUnit()[1])
+            return True
         else:
             self.Scroll(0, 0)
-        # calling Scroll sometimes doesn't raise wx.EVT_SCROLLWIN eg Windows 8 64 bit - so
-        wx.CallAfter(self.Render)
+            return False
 
     @property
     def ShowLoadProgress(self):