Allow empty radial bins in cluster ensemble

[marina-ricci]

When working with cluster ensemble we can add individual profiles to produce a stack. However, if those profiles do not have the same radial bin the stacking step will fail. This is a problem when integrating CLMM in the Cluster pipeline as we provide the same N radial bins for every cluster, but when a radial bin is empty an array N-1 will be returned. For stacking cluster_ensemble requires all profiles with the same radial bins.