MacOS job fails on the list-mode Hessian-concavity test

[KrisThielemans]

#1418 introduced Hessian calculation for the LM objective function. However, the MacOS job fails on the Hessian-concavity test (and was disabled). Also, run_test_listmode_recon.sh is not used on GHA.

The output of H*dx is 0 on MacOS, but not on other systems. I have no idea why. Most likely it doesn't read the events properly, but it does read the correct number of events, so that's hard to understand. Here's the failure diagnostics

----- testing concavity via Hessian-vector product (accumulate_Hessian_times_input)
INFO: Loaded 8019 prompts from list-mode file
INFO: Caching Additive corrections for : 8019 events.
INFO: Listmode gradient calculation: starting loop with 1 thread
INFO: Computation times for distributable_computation, CPU 0.03s, wall-clock 0.037424s
INFO: Loaded 8019 prompts from list-mode file
INFO: Caching Additive corrections for : 8019 events.
INFO: Listmode gradient calculation: starting loop with 1 thread
INFO: Computation times for distributable_computation, CPU 0.04s, wall-clock 0.037748s
Error : 0 is larger than 0, 
FAIL: PoissonLLListModeData: Computation of x^T H x = 0.000000 > 0 (Hessian) and is therefore NOT concave
 >target image max=0.999849
 >target image min=1.16359e-05
 >output image max=0
 >output image min=0

Originally posted by @KrisThielemans in #1418 (comment)