Modules: fix top-level await handling in QuickJS

Modules: fix top-level await handling in QuickJS

Previously, the result of module evaluation was awaited, but the
outcome was not checked:

  - a rejected top-level await was silently ignored;
  - a top-level await on a promise settled only by a timer or another
    asynchronous event remained pending.

In both cases the module was considered loaded without its exports
and each request failed later with a misleading "js function not
found" error.

Now, both cases fail the context creation with an explicit error.

The issue was introduced in 9a5430e6 (0.9.5).