Fix global property access crash in raw context

[bnoordhuis]

A raw context doesn't contain anything but that doesn't mean property access is allowed to crash.

Rename interrupt-test.c to the more general api-test.c and add a test.

Fixes: #914

[bnoordhuis]

It's not a complete fix yet because something like var f = () => {} still crashes because ctx->global_obj is JS_NULL and JS_DefineGlobalFunction and JS_DefineGlobalVar call JS_VALUE_GET_OBJ(ctx->global_obj) without checking it's an object first.

Adding a JS_IsObject check should add only minimal overhead so I'll guess I'll just go and do that? - edit: found a better way, just initialize the global object