catch v2 sched export before file created

https://anki.tenderapp.com/discussions/beta-testing/1210-scheduling-error#comment_45692960

aqt/exporting.py

@@ -7,7 +7,7 @@ import re
 from aqt.qt import *
 import  aqt
 from aqt.utils import getSaveFile, tooltip, showWarning, askUser, \
-    checkInvalidFilename
+    checkInvalidFilename, showInfo
 from anki.exporting import exporters
 from anki.hooks import addHook, remHook
 from anki.lang import ngettext
@@ -85,6 +85,10 @@ class ExportDialog(QDialog):
             deck_name = self.decks[self.frm.deck.currentIndex()]
             deck_name = re.sub('[\\\\/?<>:*|"^]', '_', deck_name)
 
+        if not self.isVerbatim and self.isApkg and self.exporter.includeSched:
+            showInfo("Please switch to the regular scheduler before exporting a single deck .apkg with scheduling.")
+            return
+
         filename = '{0}{1}'.format(deck_name, self.exporter.ext)
         while 1:
             file = getSaveFile(self, _("Export"), "export",