N_non_zero may depend on nf

In the current version of ALF, we assume that the number of non-zero eigenvalues of an operator is flavor independent. This does not have to be the case (note that V may depend on the flavor). This can then lead to segfaults and ill-defined behavior in the upgrade routine.

1. op_dim=N_non_zero(nf=1) < N_non_zero(nf>1) --> segfault to be expected
2. op_dim=N_non_zero(nf=1) < N_non_zero(nf>1) --> temp matrices are too large, contain uninitialzed elements --> ill-defined update.