Fix build on win32

Include/RmlUi/Core/Variant.h

@@ -148,7 +148,7 @@ private:
 	void Set(const FontEffectsPtr& value);
 	void Set(FontEffectsPtr&& value);
 	
-	static constexpr size_t LOCAL_DATA_SIZE = sizeof(TransitionList);
+	static constexpr size_t LOCAL_DATA_SIZE = (sizeof(TransitionList) > sizeof(String) ? sizeof(TransitionList) : sizeof(String));
 
 	Type type;
 	alignas(TransitionList) char data[LOCAL_DATA_SIZE];

Source/Core/StyleSheetParser.cpp

@@ -150,7 +150,7 @@ static bool IsValidIdentifier(const String& str)
 	if (str.empty())
 		return false;
 
-	for (int i = 0; i < str.size(); i++)
+	for (size_t i = 0; i < str.size(); i++)
 	{
 		char c = str[i];
 		bool valid = (