FromDataHash should not crash if hash with __ptype key is not a type

In case FromDataHash is given a hash where a key is "__ptype", and its value is not a type, it should then assume that what it is looking at is just a hash instead of crashing.

This is caused by the ToStringifiedConverter not converting to a safe form when seeing such a hash. The ToStringifyConverter should simply generate "reserved-key: __ptype" for such hashes since the result is for human consumption.