Incorrect enum constructor triggers dangling node reference error

[bbannier]

As of b098367 the following incorrect code is not rejected anymore, but instead triggers an exception at compile time:

# file: foo.spicy
module foo;

type C = enum { X, Y, };
global c = C::X(); # There is no constructor for `C::X`, instead should directly use the `C::X` literal.

$ spicyc -dj foo.spicy
libc++abi: terminating due to uncaught exception of type hilti::node_ref::Invalid: dangling node reference
[1]    50453 abort      ./bin/spicyc -dj <..>/foo.spicy

Prior to above commit this was rejected with the following

$ spicyc -dj foo.spicy
[error] <..>/foo.spicy:5:12: ID 'C::X' resolves to something other than just functions
[error] spicyc: aborting after errors