hack around the browser not closing on sync

saveNow() must run asynchronously, but unloadCollection() was not
designed to. fix the issue by skipping the save, as it's unlikely
the user can move the cursor from the editor to the
main window and start a sync before the timer has automatically saved
the contents.

aqt/browser.py

@@ -354,6 +354,7 @@ class Browser(QMainWindow):
         applyStyles(self)
         self.mw = mw
         self.col = self.mw.col
+        self.forceClose = False
         self.lastFilter = ""
         self._previewWindow = None
         self._closeEventHasCleanedUp = False
@@ -460,7 +461,7 @@ class Browser(QMainWindow):
 
     def closeEvent(self, evt):
         if not self._closeEventHasCleanedUp:
-            if self.editor.note:
+            if self.editor.note and not self.forceClose:
                 # ignore event for now to allow us to save
                 self.editor.saveNow(self._closeEventAfterSave)
                 evt.ignore()