scftorture: Account for weight_resched when checking for all zeroes

The "all zero weights makes no sense" error is emitted even when
scftorture.weight_resched is non-zero because it was left out of
the enclosing "if" condition.  This commit adds it in.

Fixes: 1ac78b49 ("scftorture: Add an alternative IPI vector")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>