Actually fix the thing I said I fixed before... (#38)

* Actually fix degenerate singular value check

* Fix attempt III

* attempt IV

* Add empty tensor check infinitepeps constructor

src/algorithms/ctmrg.jl

@@ -336,7 +336,7 @@ function left_move(state, env::CTMRGEnv{C,T}, alg::CTMRG) where {C,T}
             # Compute SVD truncation error and check for degenerate singular values
             ignore_derivatives() do
                 if alg.verbosity > 0 && is_degenerate_spectrum(S)
-                    svals = SectorDict{sectortype(S)}(c => diag(b) for (c, b) in blocks(S))
+                    svals = TensorKit.SectorDict(c => diag(b) for (c, b) in blocks(S))
                     @warn("degenerate singular values detected: ", svals)
                 end
             end

src/states/infinitepeps.jl

@@ -13,6 +13,7 @@ struct InfinitePEPS{T<:PEPSTensor} <: AbstractPEPS
             )
             space(A[d, w], 3) == space(A[d, _next(w, end)], 5)' ||
                 throw(SpaceMismatch("East virtual space at site $((d, w)) does not match."))
+            dim(space(A[d, w])) > 0 || @warn "no fusion channels at site ($d, $w)"
         end
         return new{T}(A)
     end