[bugfix] fixes bug when player asks to withdraw a string ex; "withdraw" "x"

[Coldensjo]

If you say "withdraw" "asjdhajsdhajsd" to the banker you will get this error. This PR should fix it.

Jun 04 07:29:31 Ironcore gdb[1007034]: Lua Script Error: [Npc interface]
Jun 04 07:29:31 Ironcore gdb[1007034]: data/npc/scripts/Suzy.lua:onCreatureSay
Jun 04 07:29:31 Ironcore gdb[1007034]: data/npc/lib/npc.lua:122: bad argument #1 to 'sub' (number expected, got nil)
Jun 04 07:29:31 Ironcore gdb[1007034]: stack traceback:
Jun 04 07:29:31 Ironcore gdb[1007034]: [C]: at 0x55555560ff80
Jun 04 07:29:31 Ironcore gdb[1007034]: [C]: in function 'sub'
Jun 04 07:29:31 Ironcore gdb[1007034]: data/npc/lib/npc.lua:122: in function 'getMoneyCount'
Jun 04 07:29:31 Ironcore gdb[1007034]: data/npc/scripts/Suzy.lua:140: in function 'callback'
Jun 04 07:29:31 Ironcore gdb[1007034]: data/npc/lib/npcsystem/npchandler.lua:413: in function 'onCreatureSay'
Jun 04 07:29:31 Ironcore gdb[1007034]: data/npc/scripts/Suzy.lua:10: in function <data/npc/scripts/Suzy.lua:10>

[EvilHero90]

was already tested

[EPuncker]

yo lets stick to tabs for Lua files indentation please 😄