[CSSimplify] Don't pile up fixes for incorrect optional chaining

If the contextual type propagated into the optional chain mismatches with
the inner type formed from its member references and that inner type
is a result of some fix, let's consider that un-salvageable and avoid
producing additional "ignore contextual type" fixes which only lead
to subpar solutions.

(cherry picked from commit 243cc16)

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -5425,8 +5425,14 @@ bool ConstraintSystem::repairFailures(
       auto contextualTy = simplifyType(rhs)->getOptionalObjectType();
       if (!lhs->getOptionalObjectType() && !lhs->hasTypeVariable() &&
           contextualTy && !contextualTy->isTypeVariableOrMember()) {
-        conversionsOrFixes.push_back(IgnoreContextualType::create(
-            *this, lhs, rhs, getConstraintLocator(OEE->getSubExpr())));
+        auto *fixLocator = getConstraintLocator(OEE->getSubExpr());
+        // If inner expression already has a fix, consider this two-way
+        // mismatch as un-salvageable.
+        if (hasFixFor(fixLocator))
+          return false;
+
+        conversionsOrFixes.push_back(
+              IgnoreContextualType::create(*this, lhs, rhs, fixLocator));
         return true;
       }
     }