ATLFAST2: fudge energy ratio and eta range, to avoid rare run-time crashes

This MR is to fix crashes in ART tests, as in 5372

ATLFAST2 gives a rare run-time crash when simulating photons close to the gap region. The ATLFAST2 is at the end of it's life, but we'll still want to use it a bit longer because of it's lower memory footprint. We therefore suggest to fudge the energy threshold and eta range as in this MR.

Committing the fix obo @mduehrss who proposed it.