Describe the bug
A clear and concise description of what the bug is.

Using the latest stable XTB version 6.6.1 I run into a segfault when performing a single point calculation on our cluster using GFN-FF for either of the two structures attached.
Running the same jobs on my personal laptop, I just get a warning instead of the segfault:

########################################################################
[WARNING] Runtime exception occurred
-1- gfnff_setup: Could not read topology file.
########################################################################

When I rerun these job on my laptop in the same folder, XTB is able to read the topology file produced in the first iteration.
In the attached files, I piped stdout and stderr into the respective res.out files.

To Reproduce
Steps to reproduce the behaviour:

• I use the precompiled XTB binary that I downloaded from this Github repo.
• The command I used: xtb inp.xyz --gfnff --verbose

1. happens with input (include input files)
2. start xtb with (all the options here)
3. run xtb with your options and the --verbose flag
4. output showing the error

Please provide all input and output file such that we confirm your report.

Expected behaviour
A clear and concise description of what you expected to happen.

A single point calculation without any segfaults nor any warnings.

Additional context
Add any other context about the problem here.

Based on a rough analysis, I assume the bug originates from the following code snippet obtained from the specialTorsList procedure contained in gfnff_ini.f90:

integer :: i,j,k,ii,jj,kk,ll,idx
  logical :: iiok, llok
  idx=0
  do i=1, mol%n
    ! carbon with two neighbors bonded to other carbon* with two neighbors
    if (mol%at(i).eq.6.and.topo%nb(20,i).eq.2) then
      do j=1, 2
        nbi=topo%nb(j,i)
        if (mol%at(nbi).eq.6.and.topo%nb(20,nbi).eq.2) then  ! *other carbon
          ! check carbon triple bond distance
          if (NORM2(mol%xyz(1:3,i)-mol%xyz(1:3,nbi)).le.2.37) then
            ! at this point we know that i and nbi are carbons bonded through triple bond
            ! check C2 and C3
            do k=1, 2  ! C2 is other nb of Ci
              if (topo%nb(k,i).ne.nbi.and.mol%at(topo%nb(k,i)).eq.6) then
               print *, "Setting jj"
                jj=topo%nb(k,i)
              endif
            enddo
            do k=1, 2  ! C3 is other nb of Cnbi
              if (topo%nb(k,nbi).ne.i.and.mol%at(topo%nb(k,nbi)).eq.6) then
                kk=topo%nb(k,nbi)
                print *, "Setting kk"
              endif
            enddo
            ! check C1 through C4 are sp2 carbon
            if (topo%hyb(jj).eq.2.and.topo%hyb(kk).eq.2 &
            &   .and.mol%at(jj).eq.6.and.mol%at(kk).eq.6) then

The variables jj and kk are declared, but not initialized at the beginning. I assume that the two if statements, that are meant to assign values to jj and kk, are never entered for the given examples, leaving the two variables uninitialized. Thus, in the last if statement, jj and kk end up with values beyond the size of the arrays topo%hyb and mol%at, resulting in the segfault.

Can you confirm the issue?

xtb661_issue.zip