Fi crashes when particles move too far away

**Describe the bug**
In Fi, if particles move more than 2000AU away from the stars then the code crashes with error -1.

**To Reproduce**
Eject some hydro particles (better test case TBD)

**Expected behavior**
A clear and concise description of what the problem is, so that the user is not left bewildered.

Thanks to Rik for reporting!