fix: violating strict aliasing rules in most areas in the new code.

Yes, I am aware there are plenty of violations in `conf.c`, but I'll
likely fix/rewrite those when I will use it. Since there are some other
changes I think I'll want to make.

src/dat/nbt.h

@@ -37,8 +37,8 @@ enum nbt_tagid {
 };
 
 struct nbt_array {
-	i32 len;
-	u8 dat[];
+	i32 nmemb;
+	void *dat;
 };