fix(create): accept default package name when pressing Enter without typing

When the user presses Enter on the "Package name:" prompt without typing,
`@clack/core` passes `undefined` as the value to validate. The old condition
`value != null && value.length === 0` skipped `undefined`, causing validation
to fail with "Invalid package name". Changed to `value == null || value.length
=== 0` so both `undefined` and empty string are treated as "use the default".

Author: fengmk2

packages/cli/src/create/prompts.ts

@@ -20,7 +20,7 @@ export async function promptPackageNameAndTargetDir(
       placeholder: defaultPackageName,
       defaultValue: defaultPackageName,
       validate: (value) => {
-        if (value != null && value.length === 0) {
+        if (value == null || value.length === 0) {
           return;
         }