fix: Handle Account and Item None not found in Opening Invoice Creation Tool

[marination]

Issue:

Account None not found

• The following is visible on trying to create invoices via Opening Invoice Creation Tool
  
• This happens as it tries to set the Debit To/Credit To account in Sales/Purchase Invoice
• get_party_account handles fetching this account based on Customer/Supplier
• If no account exists against Customer/Supplier or Customer Group/Supplier Group or Company then get_party_account gets no value
• frappe.db.get_value in validate_credit_to_acc gets None as an argument, hence the error

Item None not found

• If Update Item is set to default as 1(in the doctype specification), then it tried creating an SLE for such an Invoice via Opening Invoice Creation Tool
• Item Code is not set via Opening Invoice Creation Tool, this is bound to break
• Similar error for Item

Fix:

• While validating debit/credit account if it has no value , try setting it again. If still no value, prompt user to set it somewhere:
  
• Make sure no SLE creation is initiated if via Opening Invoice Creation Tool, set update_stock to 0