[FIX] website: prevent console errors when changing connectors type

Since [this commit], a new option is available on the steps block to
change the style of the connectors. Unfortunately this was causing
errors in the console. This commit makes sure that we don't have these
errors in the console anymore.

Steps to reproduce the issue:
- Drop a steps block on a page
- Change the type of the connectors

=> Errors are displayed in the developer console.

[this commit]: https://github.com/odoo/odoo/commit/aba31e9f2d8a44ce1586403f2a621a6caeed57b4

task-3069766

closes odoo/odoo#107511

X-original-commit: c1805fc5d3c3eeaa5c2edca69a6b9375f4ea1a39
Signed-off-by: Outagant Mehdi (mou) <mou@odoo.com>

addons/website/static/src/snippets/s_process_steps/options.js

@@ -171,5 +171,6 @@ options.registry.StepsConnector = options.Class.extend({
                 return `M ${0.05 * width} ${hHeight * 1.2} Q ${width / 2} ${hHeight * 1.8}, ${0.95 * width - 6} ${hHeight * 1.2}`;
             }
         }
+        return '';
     },
 });