Creating new invoice re-uses old invoice number

[stinethebean3]

When creating a new invoice manually or recurring, it automatically sets the invoice number to one that has already been used. This can create confusion for record keeping. Also when trying to edit and then miss editing the invoice number, will give the error that the number has already been used. But it will just send the old number if it is recurring.

Should use the next available number after the current highest number.

Please complete the following information:

• Crater version: 6.0.6
• PHP version: 7.4.0
• Database type and version: mariadb 10.8.3