Add a missing TM_END call when mj_fwdConstraint returns early.

PiperOrigin-RevId: 494375187
Change-Id: I013b6cdac06350a6c563fb686df9104dfb7258dd

src/engine/engine_forward.c

@@ -452,6 +452,7 @@ void mj_fwdConstraint(const mjModel* m, mjData* d) {
     mju_copy(d->qacc_warmstart, d->qacc_smooth, nv);
     mju_zero(d->qfrc_constraint, nv);
     d->solver_iter = 0;
+    TM_END(mjTIMER_CONSTRAINT);
     return;
   }