reorder: add checks for invalid function inputs

reorder: add checks for invalid function inputs

For APIs which can return an error value, do sanity checking of the input
parameters for NULL and return a suitable error value for those cases.

NOTE: The drain function is currently omitting NULL checks too, but this
function has no way to flag an error value, so checking in that case would
simply mask problems.

Reported-by: Bernard Iremonger <bernard.iremonger@intel.com>
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Bernard Iremonger <bernard.iremonger@intel.com>