9774 Error message with __error using == on tuple members

This is pretty simple. I deliberately haven't included a test case because the current error message "void has no value" is so terrible.

However, I have an forthcoming CTFE pull with a test case which will ICE if this isn't fixed.

Although this looks like a trivial bug, it's a blocker for my CTFE refactoring. Please give this a high priority.