[fix] undefined parent_component in Component.ts

This change fixes an issue in Component.ts where an error occurs when the parent_component parameter is undefined, causing the following error: "Cannot read properties of undefined (reading '$$')".

The proposed solution is to add a null check to the parent_component parameter before accessing the $$ property. 

This change ensures that the code works even when parent_component is not defined, as is the case when importing a module dynamically.

src/runtime/internal/Component.ts

@@ -97,7 +97,7 @@ export function init(component, options, instance, create_fragment, not_equal, p
 		callbacks: blank_object(),
 		dirty,
 		skip_bound: false,
-		root: options.target || parent_component.$$.root
+		root: options.target || parent_component?.$$.root
 	};
 
 	append_styles && append_styles($$.root);