Swap order of calls in gen_excit_hub_k
Swap order of calls in gen_excit_hub_k

The renorm excitation generator got into an infinite loop if there are no
available excitations from i,j as there was no check of this.  Instead
we just set hmatel to 0 in that case.

hande-qmc/hande,ruthfranklin/hande,hande-qmc/hande,hande-qmc/hande,hande-qmc/hande,hande-qmc/hande