[ConstraintSystem] Fix new "empty" locator in resolveValueMember

Author: xedin

lib/Sema/CSGen.cpp

@@ -4550,7 +4550,7 @@ swift::resolveValueMember(DeclContext &DC, Type BaseTy, DeclName Name) {
   // Look up all members of BaseTy with the given Name.
   MemberLookupResult LookupResult = CS.performMemberLookup(
       ConstraintKind::ValueMember, DeclNameRef(Name), BaseTy,
-      FunctionRefKind::SingleApply, CS.getConstraintLocator(nullptr), false);
+      FunctionRefKind::SingleApply, CS.getConstraintLocator({}), false);
 
   // Keep track of all the unviable members.
   for (auto Can : LookupResult.UnviableCandidates)