Validation not working for relative path

[veenstrajelmer]

Describe the bug
When providing a pli-file from a relative path as mdu.geometry.network, there is no validation error, while it it clearly wrong

To Reproduce

import os
import hydrolib.core.dflowfm as hcdfm

dir_output = r'.\test_model_folder' #this validates while it should not
#dir_output = r'c:\test_model_folder' #this correctly raises "OSError: [Errno -51] NetCDF: Unknown file format: b'c:\\test_model_folder\\test_model.pli'"

#create dummy file
if not os.path.exists(dir_output):
    os.mkdir(dir_output)
file_pli = os.path.join(dir_output,'test_model.pli')
with open(file_pli,'w') as f:
    f.write("""name
                1    2
                1.0    2.0
                3.0    4.0
                """)

mdu_file = os.path.join(dir_output, 'test_model.mdu')
mdu = hcdfm.FMModel()
mdu.geometry.netfile = file_pli
mdu.save(mdu_file)

Expected behavior
Also when providing a relative path, there should be an error that a pli file is not a correct network.

Version info (please complete the following information):

• OS: Spyder
• Version: main branch