Reading invalid formatted plifile should raise error instead of warning

[veenstrajelmer]

Describe the bug
Reading invalid formatted plifile should raise error instead of warning.

To Reproduce

polyfile_object = read_polyfile(file_pli,has_z_values=False)

Expected behavior
Case with comments added (not supported by hydrolib, but no issue for dflowfm kernel). I would say a # is necessary but also that is not supported.

DCSM-FM_OB_all_20181108
    5  2
-9.250000000000000E+000  4.300000000000000E+001 DCSM-FM_OB_all_20181108_0001
-9.500000000000000E+000  4.300000000000000E+001 DCSM-FM_OB_all_20181108_0002
-9.750000000000000E+000  4.300000000000000E+001 DCSM-FM_OB_all_20181108_0003
-1.000000000000000E+001  4.300000000000000E+001 DCSM-FM_OB_all_20181108_0004
-1.025000000000000E+001  4.300000000000000E+001 DCSM-FM_OB_all_20181108_0005

UserWarning: Expected a valid next point at line 2.
should raise exception of invalid formatted plifile

Case with invalid nrows in plifile

DCSM-FM_OB_all_20181108
    206    2
-9.250000000000000E+000  4.300000000000000E+001 
-9.500000000000000E+000  4.300000000000000E+001 
-9.750000000000000E+000  4.300000000000000E+001 
-1.000000000000000E+001  4.300000000000000E+001 
-1.025000000000000E+001  4.300000000000000E+001 

UserWarning: EoF encountered before the block is finished.
should raise exception of invalid formatted plifile

Case with valid formatted pli file

DCSM-FM_OB_all_20181108
    5   2
-9.250000000000000E+000  4.300000000000000E+001 
-9.500000000000000E+000  4.300000000000000E+001 
-9.750000000000000E+000  4.300000000000000E+001 
-1.000000000000000E+001  4.300000000000000E+001 
-1.025000000000000E+001  4.300000000000000E+001 

UserWarning: White space at the start of the line is ignored.
this is not to relevant to warn about, it is about the white space before '5'. Disable warning?
for the last thing, I created a separate issue: #370

Version info (please complete the following information):

• OS: Windows, Anaconda, Spyder
• Version: 0.3.0

[veenstrajelmer]

Would be nice if the last point can be resolved before 0.4, maybe as part of #34 ? Otherwise, I made a PR here: #359

[MRVermeulenDeltares]

Case with valid formatted pli file & UserWarning: White space at the start of the line is ignored, already resolved in #370

[MRVermeulenDeltares]

Discussed with Jelmer: In all cases in which the file is invalid, an exception error should be raised, instead of a warning

[arthurvd]

For completeness: @veenstrajelmer and @MRVermeulenDeltares : this morning we were discussing that for now we will NOT support reading of support point labels at the end of a data line (but don't raise an error if they are present). Coincidentally, @xldeltares has reported that she is hampered by that, see new issue #467. I will continue discussion over there and keep this issue closed (because this issue here was only about changing warning into error, regardless of what we do and do not support in pli files)