【优化】Appcenter问题修复 - PDF_Reader_Pro.KMTTSWindowController.buttonItemClick_Play

https://appcenter.ms/users/support-pdfreaderpro.com/apps/PDF-Reader-Pro-DMG/crashes/errors/4061669459u/overview

PDF Office/PDF Master/Class/PDFTools/TTS/WindowController/KMTTSWindowController.swift

@@ -338,7 +338,9 @@ class KMTTSWindowController: NSWindowController, KMTTSManagerDelegate, NSWindowD
             } else {
                 let page = self.pdfView.currentPage()
                 self.currentPageIndex = self.pdfView.currentPageIndex
-                self.startSpeakingPDFPage(page!)
+                if page != nil {
+                    self.startSpeakingPDFPage(page!)
+                }
             }
         }
     }