SdkGetTrialData not taking unit 5 into account

[MichalKs]

https://github.com/dashesy/CereLink/blob/aa1135dc005666e1c7c84e8f913c20512ed7bb4b/cbmex/cbsdk.cpp#L1929
There is a -1 error here, since units go from 0 (unsorted) to 5 inclusive. num_allocated will not count spikes sorted into unit 5. In the extreme case, when there are only unit 5 spikes on a given channel num_allocated will be 0 and no data will be received by the SDK user using SdkGetTrialData.