Fixed handling one word item name on buy/sell

[nikviktorovich]

Fixed invalid handling one word item names (e.g. Maul) on !buy or !sell. As of now, it parses the item name from !buy 5 Maul as 5 Maul instead of Maul.

Basically, the change is:

if (... && args.length > 2) { ... }

to

if (... && args.length > 1) { ... }

, but for testing purposes parsing logic moved to a separate function parseItemAndAmountFromMessage.

Apparently, the function getItemAndAmount(...) used to accept message with command included, but now all references use it as follows:
getItemAndAmount(steamID, CommandParser.removeCommand(message), this.bot, prefix);
, so the command is not included anymore.

The syntax below used instead of unpacking to make linter happy:

const name = parsedMessage.name;
let amount = parsedMessage.amount;

Fixes #1692

[idinium96]

Thank you very much, and I am sorry it takes so long for me to look into this.