fix stabsel(, grid = ...)

[hofnerb]

When using

mod <- glmboost(...)
mstop(mod) <- 1
stabsel(mod, grid = 1:10)

everything works as expected. Yet, using

mstop(mod) <- 100
stabsel(mod, grid = 1:10)

ignores the grid and runs until 100 on each stabsel fold. (spotted by A. Mayr)