`xtb/gfnff` test failure with GCC-14 in CI

[foxtran]

Detected in CI with GCC-14, Debug build with CMake on x86_64 arch.

See https://github.com/foxtran/xtb/actions/runs/14149070759/job/39639997411 (slightly modified fork: just collected some of my patches). Should be reproducible with current main branch.

Stacktrace:

Program received signal SIGFPE: Floating-point exception - erroneous arithmetic operation.

Backtrace for this error:
#0  0x7f4517e23e59 in ???
#1  0x7f4517e22e75 in ???
#2  0x7f451564532f in ???
#3  0x556c77e34032 in __xtb_gfnff_eg_MOD_gfnff_eg._omp_fn.8
	at /home/runner/work/xtb/xtb/src/gfnff/gfnff_eg.f90:732
#4  0x7f45181f3976 in ???
#5  0x556c77e0c532 in __xtb_gfnff_eg_MOD_gfnff_eg
	at /home/runner/work/xtb/xtb/src/gfnff/gfnff_eg.f90:721
#6  0x556c77da8e3b in __xtb_gfnff_calculator_MOD_singlepoint
	at /home/runner/work/xtb/xtb/src/gfnff/calculator.f90:249
#7  0x556c77d319d7 in __xtb_prog_main_MOD_xtbmain
	at /home/runner/work/xtb/xtb/src/prog/main.F90:705
#8  0x556c77d390b2 in xtb_prog_primary
	at /home/runner/work/xtb/xtb/src/prog/primary.f90:57
#9  0x556c77d3918d in main
	at /home/runner/work/xtb/xtb/src/prog/primary.f90:20