When creating a star from gas, also synchronise the drifting points.

src/runner.c

@@ -556,6 +556,7 @@ void runner_do_star_formation(struct runner *r, struct cell *c, int timer) {
 
 #ifdef SWIFT_DEBUG_CHECKS
           sp->ti_kick = gp->ti_kick;
+          gp->ti_drift = sp->drift;
 #endif
 
           /* Set a smoothing length */