checker: fix C struct embedded init fields checking

[felipensp]

Fix #21046

#include "@VMODROOT/foo.h"

struct C.MyCStruct {
	data &u8
}

struct MyWrapper {
	C.MyCStruct
}

fn (it C.MyCStruct) wrap() MyWrapper {
	return MyWrapper{
		//MyCStruct: it
		data: it.data
	}
}

fn main() {
	dump(C.MyCStruct{data: 123}.wrap())
}

[spytheman]

Can you add a test please?

[felipensp]

Can you add a test please?

Done.

[spytheman]

Excellent work.