[yaml2obj] - Don't crash on one more invalid document.

[grimar]

Summary

This fixes one more crash I faced.
Testcase contains minimal reduced case.

Note: there is also D38039 which refactors whole createHNodes method
to make it more readable, it is independent improvement though.

[grimar]

• Fixed last minute renaming mistake.

lib/Support/YAMLTraits.cpp

for (Node &SN : *SQ) {
         break;
       SQHNode->Entries.push_back(std::move(Entry));
     }
     return std::move(SQHNode);
   } else if (MappingNode *Map = dyn_cast<MappingNode>(N)) {
     auto mapHNode = llvm::make_unique<MapHNode>(N);
     for (KeyValueNode &KVN : *Map) {
       Node *KeyNode = KVN.getKey();
-      ScalarNode *KeyScalar = dyn_cast<ScalarNode>(KeyNode);
-      if (!KeyScalar) {
+      ScalarNode *Key = dyn_cast<ScalarNode>(KeyNode);
+      Node *Value = KVN.getValue();
+      if (!Key || !Value) {
+        if (!Key)
           setError(KeyNode, "Map key must be a scalar");
+        if (!Value)
+          setError(KeyNode, "Map value must not be empty");
         break;
       }
       StringStorage.clear();
-      StringRef KeyStr = KeyScalar->getValue(StringStorage);
+      StringRef KeyStr = Key->getValue(StringStorage);
       if (!StringStorage.empty()) {
         // Copy string to permanent storage
         KeyStr = StringStorage.str().copy(StringAllocator);
       }
-      auto ValueHNode = this->createHNodes(KVN.getValue());
+      auto ValueHNode = this->createHNodes(Key);
       if (EC)
         break;
       mapHNode->Mapping[KeyStr] = std::move(ValueHNode);
     }
     return std::move(mapHNode);
   } else if (isa<NullNode>(N)) {
     return llvm::make_unique<EmptyHNode>(N);
   } else {

test/Object/yaml2obj-invalid.yaml

+AAA: | BBB
+
+# RUN: not yaml2obj %s 2>&1 | FileCheck %s
+# CHECK: Map value must not be empty