minor bug fixed (md_val)

error array lengths

src/juobs_tools.jl

@@ -352,7 +352,7 @@ function md_val(a::uwreal, obs::Corr, derm::Vector{Corr})
         fluc_ow = vcat(fluc_ow'...)
         ow_data = ow_mean .+ ws.fluc[n_ow]
         =#
-        der = a.der[n_ow] * w_mean
+        der = length(a.der) >= maximum(n_ow) ? a.der[n_ow] * w_mean : 0.0
     else
         return nothing
     end