[Diagnostics] Don't assume that contextual type for optional chain is optional

While checking validity of the optional chain, let's not assume
that the contextual type associated with is optional because
enclosing expression could too be invalid.

Resolves: rdar://85166519

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -4060,7 +4060,7 @@ bool ConstraintSystem::repairFailures(
       // optionality if needed.
       auto contextualTy = simplifyType(rhs)->getOptionalObjectType();
       if (!lhs->getOptionalObjectType() && !lhs->hasTypeVariable() &&
-          !contextualTy->isTypeVariableOrMember()) {
+          contextualTy && !contextualTy->isTypeVariableOrMember()) {
         conversionsOrFixes.push_back(IgnoreContextualType::create(
             *this, lhs, rhs, getConstraintLocator(OEE->getSubExpr())));
         return true;

test/Constraints/optional.swift

@@ -499,3 +499,13 @@ func rdar75514153() {
   test_labeled(42, x: nil)   // expected-error {{no exact matches in call to local function 'test_labeled'}}
   test_labeled(42, x: (nil)) // expected-error {{no exact matches in call to local function 'test_labeled'}}
 }
+
+// rdar://85166519 - Crash dereferencing Null Type In Bogus Expression
+func rdar85166519() {
+  var v: Int? = nil
+
+  var _: [Int: AnyObject] = [ // expected-error {{dictionary of type '[Int : AnyObject]' cannot be initialized with array literal}}
+    // expected-note@-1 {{did you mean to use a dictionary literal instead?}}
+    v?.addingReportingOverflow(0) // expected-error {{cannot convert value of type '(partialValue: Int, overflow: Bool)?' to expected dictionary key type 'Int'}}
+  ]
+}