rt_setshims leaks previously allocated shims on partial allocation failure

Summary

rt_setshims(:1374-1391): if rt_shim[1] or [2] alloc fails after [0] allocated, no cleanup of earlier shims. rt_free does not check partial population. Slow M_RTABLE memory leak amplifying memory pressure. Fix together with DF-0397: R_Free rt_shim[0..i-1] on failure.