frontend: fix InlineParameterEditor not displaying zero values

The truthiness check `if (this.param?.value)` treated 0 as falsy,
so `internal_new_value_as_string` was never set and the field showed
the placeholder label instead of "0". Use `this.param != null` to
check for parameter existence regardless of its value.

Made-with: Cursor

Author: Williangalvani

core/frontend/src/components/parameter-editor/InlineParameterEditor.vue

@@ -322,7 +322,7 @@ export default Vue.extend({
           .map((value) => parseFloat(value))
           .includes(this.internal_new_value)
       }
-      if (this.param?.value) {
+      if (this.param != null) {
         this.internal_new_value_as_string = this.internal_new_value.toString()
       }