[Sema] Always cache the unresolved chain base

Even when we’ve already visited the expression for constraint generation (signified by the presence of an UnresolvedMemberChainResultExpr) we should still cache the chain base.

Author: Jumhyn

lib/Sema/CSGen.cpp

@@ -3845,8 +3845,8 @@ namespace {
       auto *parent = Parent.getAsExpr();
       if (isMemberChainTail(expr, parent)) {
         if (auto *UME = getUnresolvedMemberChainBase(expr)) {
+          CG.setUnresolvedChainBase(expr, UME);
           if (!parent || !isa<UnresolvedMemberChainResultExpr>(parent)) {
-            CG.setUnresolvedChainBase(expr, UME);
             auto &context = CG.getConstraintSystem().getASTContext();
             expr = new (context) UnresolvedMemberChainResultExpr(expr);
           }