React to initialValue even if initially undefined on Select.

Move the check for `undefined` into the effect itself. This enables the
`initialValue` to be changed from the default (`undefined`) later and
still have the `Select` component react to that.

Note this is done only for the `Select` component as `undefined` is
not a valid value to pass to `setValue` in the core. Supporting it would
introduce complexity because a `multiple` value should always be an
Array.

Author: martinpengellyphillips

src/select.tsx

@@ -63,14 +63,12 @@ const Select = (props: SelectProps) => {
   );
   const select = createSelect(selectProps);
 
-  if (local.initialValue !== undefined) {
-    createEffect(
-      on(
-        () => local.initialValue,
-        (value) => select.setValue(value)
-      )
-    );
-  }
+  createEffect(
+    on(
+      () => local.initialValue,
+      (value) => value !== undefined && select.setValue(value)
+    )
+  );
 
   return (
     <Container