[FIX] compiler: do not look up ComponentNode in the context

With the introduction of t-call-context, there is now no guarantee that
the ComponentNode can be found in the rendering context, any attempt to
do so can crash when combined with t-call-context. This commit fixes
that by using `this` instead, which in compiled templates refers to the
component that is being rendered.

tests/helpers.ts

@@ -96,7 +96,7 @@ export function renderToBdom(template: string, context: any = {}, node?: any): B
     createComponent() {},
     createDynamicComponent() {},
   };
-  return fn(app as any, blockDom, helpers)(context, node);
+  return fn(app as any, blockDom, helpers).call(context, context, node);
 }
 
 export function renderToString(template: string, context: any = {}, node?: any): string {