Fix crash when assiging to a property with an invalid type

This is a regression from clang 3.4

Set the result to ExprError and returns true, rather than simply
returns false because errors have been reported already and returning
false show a confusing error

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@214734 91177308-0d34-0410-b5e6-96231b3b80d8