Fix preprocess_interpolate_nc_to_bc.py

[veenstrajelmer]

The below code raises "OutOfRangeError: requested tstop 2012-04-01 12:00:00 outside of available range 2012-01-16 12:00:00 to 2012-03-16 12:00:00.". The timestep is available in the original dataset, but there is some odd timestepping (daily, but alternating midnight and midday). Either way, the time slicing is too tight for this usecase and it would be nice to resolve this to be backwards compatible.

MWE:

import os
import dfm_tools as dfmt

file_pli = r'p:\archivedprojects\11208054-004-dcsm-fm\models\model_input\bnd_cond\pli\DCSM-FM_OB_all_20181108.pli'
tstart = '2012-01-16 12:00'
tstop = '2012-04-01 12:00'
dir_sourcefiles_waq = r'p:\archivedprojects\11206304-futuremares-rawdata-preps\python_scripts\ocean_boundaryCMEMS\data_monthly'
dir_pattern = os.path.join(dir_sourcefiles_waq,'cmems_mod_glo_bgc_my_0.25_P1M-m_{ncvarname}_*.nc') 

#open regulargridDataset and do some basic stuff (time selection, renaming depth/lat/lon/varname, converting units, etc)
data_xr_vars = dfmt.open_dataset_extra(dir_pattern=dir_pattern, quantity='tracerbndNO3',
                                       tstart=tstart, tstop=tstop)

This issue might be related to #797