ensure user doesn't try to export into data folder

https://anki.tenderapp.com/discussions/ankidesktop/39008-export-path-accidentally-set-to-collectionmedia-possible-damage

qt/aqt/exporting.py

@@ -1,6 +1,8 @@
 # Copyright: Ankitects Pty Ltd and contributors
 # License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
+from __future__ import annotations
+
 import os
 import re
 import time
@@ -15,7 +17,7 @@ from aqt.utils import checkInvalidFilename, getSaveFile, showWarning, tooltip
 
 
 class ExportDialog(QDialog):
-    def __init__(self, mw, did: Optional[int] = None, cids: Optional[List[int]] = None):
+    def __init__(self, mw: aqt.main.AnkiQt, did: Optional[int] = None, cids: Optional[List[int]] = None):
         QDialog.__init__(self, mw, Qt.Window)
         self.mw = mw
         self.col = mw.col
@@ -118,6 +120,9 @@ class ExportDialog(QDialog):
                 return
             if checkInvalidFilename(os.path.basename(file), dirsep=False):
                 continue
+            if os.path.commonprefix([self.mw.pm.base, file]) == self.mw.pm.base:
+                showWarning("Please choose a different export location.")
+                continue
             break
         self.hide()
         if file: