fixed customIndices2Array forgetting first index

In !765 (merged) i made sure the overload for customIndices2Array was picking up the first element separately to disambiguate the empty case. But I forgot to put this first element into the newly created array. Since this only affects the tensor module, running the smoke tests did not reveal the problem.

I'm currently running ./check.sh ".*tensor.*" to check that this fix really helps.