Stack overflow when declaring a struct with a member being a pointer to itself

[mhasel]

When trying to compile the following

TYPE Node : STRUCT
    id      : DINT;
    child   : REF_TO Node;
    parent  : REF_TO Node;
END_STRUCT END_TYPE

the compiler will crash with a stack overflow.

A quick git bisect has shown this bug slipped in with commit 28b6b41