Crest single point and optimization segfault for GFN0 on atoms

[jevandezande]

CREST segfaults for the following, where geom.xyz contains a single atom (tested multiple open and closed shell):

crest geom.xyz --sp --gfn0
crest geom.xyz --optimize --gfn0

But not if gfnff, gfn1, or gfn2 are selected

Version 3.0.1

[pprcht]

According to the segfault that is technically an issue for https://github.com/pprcht/gfn0
But since it will end up with me anyways, I'll take care of it.

[pprcht]

I just fixed it in the gfn0 project. Will update the corresponding submodule once I looked into #320.

[pprcht]

same here, #322 should implement the fix