【分屏视图】打开一个普通文档，再打开一个加密文档，滑动页面概率性崩溃，后者滑动页面切换分屏模式必现崩溃 -- 修复

PDF Office/PDF Master/Class/PDFWindowController/PDFListView/Split/View/KMSecondaryPDFView.swift

@@ -614,7 +614,9 @@ class KMSecondaryPDFView: CPDFListView {
     }
     
     @objc func handlePageChangedNotification(_ notification: Notification) {
-        self.pagePopUpButton?.selectItem(at: self.currentPageIndex)
+        if !self.document.isLocked {
+            self.pagePopUpButton?.selectItem(at: self.currentPageIndex)
+        }
     }
     
     @objc func handleSynchronizedScaleChangedNotification(_ notification: Notification) {