Agent.valMemory and validate()

[lake4790k]

In the Agent there is a valMemory filled, but when validation() prepares the indices that reference valMemory and calls learn(), there the indices are always used with memory and not valMemory.

I assume the intention was to use valMemory when called from validate().

Not much of an issue, only makes a difference for prioritised replay, otherwise memory and valMemory have the same data anyway.