Force InputFld to update fielddef
This forces InputFld to update fielddef after loading the expansions, instead of only doing this when range is specified. This is necessary because the number of partitions from the original file might not be the same as the number of processes being used in FieldConvert, causing the fielddef obtained from Import to contain extra elements.
For example, when converting a serial fld to a parallel format using
mpirun -np 8 FieldConvert file.xml file_serial.fld file_par.fld
the current implementation causes all 8 partition files from file_par.fld to contain the whole field.