[clang] [clang][ObjC][CodeComplete] Fix crash on C-Style cast with parenthesized operand in ObjC++ (PR #180343)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

@AaronBallman @cor3ntin this is another variant of https://github.com/llvm/llvm-project/pull/177096 -- the underlying issue is that when a paren expression fails to parse we emit an error (which kills the build) but does not mark the resulting expression as being invalid - do either of you know if that is actually intentional? (I assumed it was to do with avoiding run on errors but as an approach that seems surprising?)

I think the correct fix is to make ParseParenExpression mark the result as invalid, otherwise I think we're just going to be hunting down these forever, and every need call that gets added will need to know that isInvalid is insufficient

https://github.com/llvm/llvm-project/pull/180343