simplify truncationerror implementation

Author: lkdvos

src/factorizations/truncation.jl

@@ -282,9 +282,8 @@ MAK.truncation_error(values::SectorDict, ind) =
     MAK.truncation_error!(SectorDict(c => copy(v) for (c, v) in values), ind)
 
 function MAK.truncation_error!(values::SectorDict, ind)
-    for (c, v) in values
-        ind_c = get(ind, c, nothing)
-        isnothing(ind_c) && continue
+    for (c, ind_c) in ind
+        v = values[c]
         v[ind_c] .= zero(eltype(v))
     end
     return TensorKit._norm(values, 2, zero(real(eltype(valtype(values)))))