Fixes service borgs

Created by: unid15

@DeityLink #6577 you dun goofed

    if (sent_amount > 0 && isrobot(user))
        var/mob/living/silicon/robot/borg = user
        if (!istype(borg.module, /obj/item/weapon/robot_module/butler) || !borg.cell)
            return

        var/charge_amount = max(30, 4*sent_amount)
        borg.cell.use(charge_amount)

        user << "Now synthesizing [sent_amount] units of [refill_name]..."
        spawn(300)
            reagents.add_reagent(refill_id, sent_amount)
            user << "<span class='notice'>Cyborg [src] refilled with [refill_name] ([sent_amount] units).</span>"

☝ sent_amount was -10 when transfer was successful, and 1 when it wasn't

Fixes #6624 (closed)