output_pin: Fix handling of template rendering errors

Make sure to assign 'value' on a rendering error to avoid an internal
error.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/extras/output_pin.py

@@ -228,6 +228,7 @@ class PrinterOutputPin:
             value = float(text)
         except ValueError as e:
             logging.exception("output_pin template render error")
+            value = 0.
         self.gcrq.send_async_request(value)
     cmd_SET_PIN_help = "Set the value of an output pin"
     def cmd_SET_PIN(self, gcmd):