TPropertyValueIterator skips TMap values when KeyType is a UStruct

From https://udn.unrealengine.com/questions/431271/tpropertyvalueiterator-skips-tmap-values-when-keyt.html

The property value iterator has logic where it tries to iterate over all properties in a structure, including properties nested inside structs and containers. A licensee found a problem where if you have a TMap<Struct,int> it would skip the int properties due to the way the iteration happens.

I'll fix this and also add an automated test to validate this continues to work 

1. Compile and Load EngineTest
2. Run the Project.Engine.PropertyIterator automated test and validate it succeeds, I built this into it

Or use the steps outlined in the UDN