plot_GrowthCurve() ... error for LambertW and alternate mode

[RLumSK]

Describe the bug
Throw an unexpected error on standard evaluation.
Reported by @Eiskeil via e-mail.

Please add a minimalistic reproducible example

library(Luminescence)
data(ExampleData.LxTxData, envir = environment())
temp <- plot_GrowthCurve(LxTxData, fit.method = "LambertW", mode = "alternate")
get_RLum(temp)

Expected behaviour
No error.

[RLumSK]

Fixed.