Protect makeTriplets against division by zero
A division by zero was caught in https://gitlab.cern.ch/lhcb/Allen/-/blob/master/device/SciFi/hybridseeding/src/seed_xz.cu#L159 in tests on data with a ubsan build. This MR protects against divisions by zero in the makeTriplets algorithm. Repeating locally the tests, no other zero-divison errors appear.
Closes issue MooreOnline#29 (closed)