Minor Lua Fixes (CONS_Printf and mobj_t.valid)

Let CONS_Printf be called outside a level. Is there a reason this isn't allowed??

Let mobj_t.valid be accessed outside a level (returning false of course). Got a script with this in it:

if p.realmo and p.realmo.valid

that gave a warning on intermission because apparently p.realmo still existed in Lua but ISLEVEL triggered trying to check p.realmo.valid.