qt transaction_dialog: normal close if user presses Esc

(Electron-Cash/Electron-Cash#890)

electrum/gui/qt/transaction_dialog.py

@@ -178,6 +178,10 @@ class TxDialog(QDialog, MessageBoxMixin):
             except ValueError:
                 pass  # was not in list already
 
+    def reject(self):
+        # Override escape-key to close normally (and invoke closeEvent)
+        self.close()
+
     def show_qr(self):
         text = bfh(str(self.tx))
         text = base_encode(text, base=43)