Load(): Bug when loading some datasets, Load() crashes.

As @rcruzgar and @eexarchou reported:

Loading for example, 'i025', makes Load() crash with the error

Error in sort.list(x, decreasing = decreasing) : 
  argument 1 is not a vector
In addition: Warning message:
In is.na(x) : is.na() applied to non-(list or vector) of type 'NULL'

Also, ice variables 'sie_.*' not found for 'nsidc-nasa' or 'hadisst_v1.1'.