Fix corner case in zero-dim broadcast

Author: mtfishman

src/blocksparsearrayinterface/broadcast.jl

@@ -40,7 +40,8 @@ end
 # If the RHS is zero, this makes sure that the storage is emptied,
 # which is logic that is handled by `fill!`.
 function copyto_blocksparse!(dest::AbstractArray, bc::Broadcasted{<:AbstractArrayStyle{0}})
-  value = bc.f(bc.args...)
+  # `[]` is used to unwrap zero-dimensional arrays.
+  value = bc.f(bc.args...)[]
   return @interface BlockSparseArrayInterface() fill!(dest, value)
 end