Add matching fix for PrettyWriter

PrettyWriter EndObject will now also assert if called when a key is
missing its matching value.

include/rapidjson/prettywriter.h

@@ -136,8 +136,10 @@ public:
 	
     bool EndObject(SizeType memberCount = 0) {
         (void)memberCount;
-        RAPIDJSON_ASSERT(Base::level_stack_.GetSize() >= sizeof(typename Base::Level));
-        RAPIDJSON_ASSERT(!Base::level_stack_.template Top<typename Base::Level>()->inArray);
+        RAPIDJSON_ASSERT(Base::level_stack_.GetSize() >= sizeof(typename Base::Level)); // not inside an Object
+        RAPIDJSON_ASSERT(!Base::level_stack_.template Top<typename Base::Level>()->inArray); // currently inside an Array, not Object
+        RAPIDJSON_ASSERT(0 == Base::level_stack_.template Top<typename Base::Level>()->valueCount % 2); // Object has a Key without a Value
+       
         bool empty = Base::level_stack_.template Pop<typename Base::Level>(1)->valueCount == 0;
 
         if (!empty) {

test/unittest/prettywritertest.cpp

@@ -207,6 +207,57 @@ TEST(PrettyWriter, RawValue) {
         buffer.GetString());
 }
 
+TEST(PrettyWriter, InvalidEventSequence) {
+    // {]
+    {
+        StringBuffer buffer;
+        PrettyWriter<StringBuffer> writer(buffer);
+        writer.StartObject();
+        EXPECT_THROW(writer.EndArray(), AssertException);
+        EXPECT_FALSE(writer.IsComplete());
+    }
+    
+    // [}
+    {
+        StringBuffer buffer;
+        PrettyWriter<StringBuffer> writer(buffer);
+        writer.StartArray();
+        EXPECT_THROW(writer.EndObject(), AssertException);
+        EXPECT_FALSE(writer.IsComplete());
+    }
+    
+    // { 1:
+    {
+        StringBuffer buffer;
+        PrettyWriter<StringBuffer> writer(buffer);
+        writer.StartObject();
+        EXPECT_THROW(writer.Int(1), AssertException);
+        EXPECT_FALSE(writer.IsComplete());
+    }
+    
+    // { 'a' }
+    {
+        StringBuffer buffer;
+        PrettyWriter<StringBuffer> writer(buffer);
+        writer.StartObject();
+        writer.Key("a");
+        EXPECT_THROW(writer.EndObject(), AssertException);
+        EXPECT_FALSE(writer.IsComplete());
+    }
+    
+    // { 'a':'b','c' }
+    {
+        StringBuffer buffer;
+        PrettyWriter<StringBuffer> writer(buffer);
+        writer.StartObject();
+        writer.Key("a");
+        writer.String("b");
+        writer.Key("c");
+        EXPECT_THROW(writer.EndObject(), AssertException);
+        EXPECT_FALSE(writer.IsComplete());
+    }
+}
+
 #if RAPIDJSON_HAS_CXX11_RVALUE_REFS
 
 static PrettyWriter<StringBuffer> WriterGen(StringBuffer &target) {