reactive: fix typo/bug in reactive_ops.__call__ (#1069)

Author: ypsah

param/reactive.py

@@ -230,7 +230,7 @@ def _as_rx(self):
     def __call__(self) -> 'rx':
         """Create a reactive expression."""
         rxi = self._reactive
-        return rxi if isinstance(rx, rx) else rx(rxi)
+        return rxi if isinstance(rxi, rx) else rx(rxi)
 
     def and_(self, other) -> 'rx':
         """