[AST] "Simple case" of specialized conditional requirements should be an optional with an empty array.

Author: huonw

lib/AST/ProtocolConformance.cpp

@@ -861,7 +861,7 @@ void SpecializedProtocolConformance::computeConditionalRequirements() const {
     auto &ctxt = getProtocol()->getASTContext();
     ConditionalRequirements = ctxt.AllocateCopy(newReqs);
   } else {
-    ConditionalRequirements = {};
+    ConditionalRequirements = ArrayRef<Requirement>();
   }
 }