[Bugfix] SDPReceiveVertex reserved too little space for output keys.
[Bugfix] SDPReceiveVertex reserved too little space for output keys.

(cherry picked from commit a3d7ddb62bb446f3eef9abef78c467d7d2c9da54)

ctn-archive/nengo_spinnaker_2014,ctn-archive/nengo_spinnaker_2014,ctn-archive/nengo_spinnaker_2014,ctn-archive/nengo_spinnaker_2014