The 'GroupOutputs()' function performs the same
calculations for only-positive and mixed groups,
the only difference is that when we look for
only-positive groups, we discard negative utxos.
So, instead of wasting resources calling GroupOutputs()
for positive-only first, then call it again to include
the negative ones in the result, we can execute
GroupOutputs() only once, including in the response
both group types (positive-only and mixed).