fix: Empty edge handling in softmax_edge_neighbors (#636)

* fix: Set init in `softmax_edge_neighbors`

* fix: Dimension consistency

Author: lenianiva

GNNlib/src/utils.jl

@@ -90,6 +90,9 @@ function softmax_edge_neighbors(g::AbstractGNNGraph, e)
         @assert size(e)[end] == g.num_edges
     end
     s, t = edge_index(g)
+    if isempty(t)
+        return zeros_like(e, eltype(e), (size(e)[1:end-1]..., 0))
+    end
     max_ = gather(scatter(max, e, t), t)
     num = exp.(e .- max_)
     den = gather(scatter(+, num, t), t)