fix: prevent unnecessary db.commit for contact insert

[HarryPaulo]

We have ERPNext integrated with another system, when retrieving data from the other system, the following is created:
Customer
Addresses
Contacts
The link between the two systems has been created

When we synchronize, a for loop is performed and the customer, address and contact are inserted, but there may be errors in the process...

When there are errors, a rollback must be performed, but when inserting the contact, ERPNext executes an "after_insert" hook event calling the erpnext.telephony.doctype.call_log.call_log.link_existing_conversations method
thus executing frappe.db.commit()

Two improvements were made:

1. Only perform frappe.db.commit if there is an impact record returned by the select above.

2. Created an "ignore_auto_link_call_log" flag to ignore this method when we do not want it to execute, as this commit may break the code.