Fix applyFolds for irregular grid

[davidruegamer]

The following lines are now removed from the FDboost help as they throw an error :

  ## Find optimal mstop, small grid/low B for a fast example
  set.seed(123)
  folds4 <- cv(rep(1, length(unique(mod4$id))), B = 3)
  appl4 <- applyFolds(mod4, folds = folds4, grid = 1:50)
  ## val4 <- validateFDboost(mod4, folds = folds4, grid = 1:50)

  set.seed(123)
  folds4long <- cvLong(id = mod4$id, weights = model.weights(mod4), B = 3)
  cvm4 <- cvrisk(mod4, folds = folds4long, grid = 1:50)
  mstop(cvm4)

@Almond-S found that this is related to applyFold which does not work correctly with irregular data