leave max_button pressed (fix #5251)

electrum/gui/qt/paytoedit.py

@@ -152,11 +152,11 @@ class PayToEdit(CompletionTextEdit, ScanQRTextEdit, PrintError):
             else:
                 total += output.value
 
-        self.win.is_max = is_max
+        self.win.max_button.setChecked(is_max)
         self.outputs = outputs
         self.payto_address = None
 
-        if self.win.is_max:
+        if self.win.max_button.isChecked():
             self.win.do_update_fee()
         else:
             self.amount_edit.setAmount(total if outputs else None)