E-book viewer: Fix viewer not closing on SIGINT. Fixes #2099777 [ebook-viewer refuses to die after ctrl+c](https://bugs.launchpad.net/calibre/+bug/2099777)

src/calibre/gui2/viewer/main.py

@@ -155,6 +155,7 @@ def run_gui(app, opts, args, internal_book_data, listener=None):
         open_at=opts.open_at, continue_reading=opts.continue_reading, force_reload=opts.force_reload,
         calibre_book_data=internal_book_data)
     main.set_exception_handler()
+    app.shutdown_signal_received.connect(main.request_close)
     if len(args) > 1:
         acc.events.append(os.path.abspath(args[-1]))
     acc.got_file.connect(main.handle_commandline_arg)

src/calibre/gui2/viewer/ui.py

@@ -811,6 +811,9 @@ class EbookViewer(MainWindow):
             self.cfi_changed(cfi)
         self.force_close()
 
+    def request_close(self):
+        self.close()
+
     def closeEvent(self, ev):
         if self.shutdown_done:
             return