Fix issue 8982 ICE(ctfeexpr.c) __parameters of an erroneous default parameter

Don't create a tuple with an error in it; instead, return an ErrorExp.
This is the same behaviour you get when creating a erroneous tuple by normal means.

(The test case is wrapped in a speculative template so that the module compiles even though
it contains an error).
Merge pull request #1453 from donc/ice8982ctfe__parameters

8982 ICE(ctfeexpr.c) __parameters of an erroneous default parameter
Fixes Issue 1369 - getMember doesn't work for aggregate variables.