Adds safety asserts.

Reflection/Struct.hpp

@@ -9,6 +9,7 @@
 #ifndef Struct_hpp
 #define Struct_hpp
 
+#include <cassert>
 #include <cstdarg>
 #include <cstring>
 #include <string>
@@ -113,6 +114,15 @@ struct Serialisable {
 
 template <typename Owner> class StructImpl: public Struct {
 	public:
+#ifndef NDEBUG
+		StructImpl() {
+			// Protect against declarations that nominate the wrong Owner; this isn't
+			// a static assert because that wouldn't catch all invalid cases.
+			const auto owner = static_cast<Owner *>(this);
+			assert(owner != nullptr);
+		}
+#endif
+
 		/*!
 			@returns the value of type @c Type that is loaded from the offset registered for the field @c name.
 				It is the caller's responsibility to provide an appropriate type of data.