[X] check for null on the parent property (#5796)

In case of value types in Compiled Binding Paths, we weren't checking
for null property on the right part of the path

before
```csharp
bindingExtension.TypedBinding = new TypedBinding<Gh5770, Color>(delegate(Gh5770 gh)
	{
		if (gh == null)
		{
			return new ValueTuple<Color, bool>(default(Color), false);
		}
		Gh5770VM expr_24 = gh.MyContentViewModel;
		return new ValueTuple<Color, bool>(expr_24.TextColor, true);
	}, ..., ...);
```

after
```csharp
bindingExtension.TypedBinding = new TypedBinding<Gh5770, Color>(delegate(Gh5770 gh)
	{
		if (gh == null)
		{
			return new ValueTuple<Color, bool>(default(Color), false);
		}
		Gh5770VM expr_24 = gh.MyContentViewModel;
		if (expr_24 == null)
		{
			return new ValueTuple<Color, bool>(default(Color), false);
		}
		return new ValueTuple<Color, bool>(expr_24.TextColor, true);
	}, ..., ...);
```

- fixes #5770

Xamarin.Forms.Build.Tasks/SetPropertiesVisitor.cs

@@ -549,7 +549,7 @@ namespace Xamarin.Forms.Build.Tasks
 						il.Emit(Ldloca, loc);
 					}
 
-					if (!property.PropertyType.IsValueType) { //if part of the path is null, return (default(T), false)
+					if (!propDeclTypeRef.IsValueType) { //if part of the path is null, return (default(T), false)
 						var nop = Create(Nop);
 						il.Emit(Dup);
 						il.Emit(Ldnull);