crest with gfnff for intermolecular complexes has problem with charges

[robpollice]

Describe the bug
Crest crashes when GFN-FF is used for intermolecular complexes together with specification of charge and/or multiplicity. I am using the pre-compiled version 2.10.1 together with the pre-compiled version 6.3.0 of xtb. Here are the files: xtb.zip

To Reproduce
Steps to reproduce the behaviour:

1. XYZ with more than one molecule (see mol.xyz in the example).
2. Run crest mol.xyz -chrg 0 -uhf 0 -gfnff -nci -mquick -opt loose and the job crashes.
3. The outputs crest.out and xtb.out are provided in the ZIP file.
4. Run crest mol.xyz -gfnff -nci -mquick -opt loose and everything runs fine (after purging the folder of files from the previous run).

[pprcht]

It seems to be that GFN-FF calculations fail in xtb if there is a .CHRG file with a specified molecular charge of 0 because it will produce a EEQ charge constrain error. This should be fixed with the upcoming xtb 6.3.1 version.

For now please just refrain from using -chrg 0 as a command line argument. The molecular charge of 0 is the default assumption and does not need specification.