fix sorting problem

Author: lkdvos

src/implementations/truncation.jl

@@ -137,7 +137,8 @@ function truncation_error(values::AbstractVector{<:Number}, ind::AbstractVector{
     return sqrt(init)
 end
 function truncation_error(values::AbstractVector{<:Number}, ind::AbstractVector{<:Integer})
-    sort!(ind)
+    !issorted(ind) && return @invoke truncation_error(values::AbstractVector, ind)
+
     allind = eachindex(IndexLinear(), values)
     next_i, next_j = iterate(allind), iterate(ind)
     init = abs2(zero(eltype(values)))
@@ -154,6 +155,5 @@ function truncation_error(values::AbstractVector{<:Number}, ind::AbstractVector{
         @inbounds init += abs2(values[i])
         next_i = iterate(allind, state_i)
     end
-
     return sqrt(init)
 end