Return 1 when the user cancelled

So, cancelling can be seen as a failure to the original goal, entering a
character. And distinguising it from the true success case is helpful
for scripting `rofimoji`, so now it return `1` when the user cancelled.

Issue: #232

Author: fdw

src/picker/standalone.py

@@ -25,7 +25,7 @@ def standalone(self) -> None:
         action, value = self.__open_main_selector_window()
 
         if action == CANCEL():
-            sys.exit()
+            sys.exit(1)
         elif action != DEFAULT():
             self.args.actions = [action]