Don't log a warning in GetPropertyHelper when the property isn't
present. The function returns an optional, so any callers that want to
log a warning when nullopt is returned can do so themselves.
This prevents plugged-in devices (an Xbox One controller in my case)
from spamming the message "W[COMMON]: CM_Get_DevNode_Property returned:
37" twice per second (that value being CR_NO_SUCH_VALUE).
