fix: do not update qty if already set

[s-aga-r]

Related: https://github.com/frappe/erpnext/pull/38608

[stale[bot]]

This pull request has been automatically marked as inactive because it has not had recent activity. It will be closed within 3 days if no further activity occurs, but it only takes a comment to keep a contribution alive :) Also, even if it is closed, you can always reopen the PR when you're ready. Thank you for contributing.

[GopalKedia2020]

Is there any Work in Progress for this issue? The issue was raised by me using the ticket no 6766 in frappe support and i am seeing this solution in draft from long time.

[stale[bot]]

This pull request has been automatically marked as inactive because it has not had recent activity. It will be closed within 3 days if no further activity occurs, but it only takes a comment to keep a contribution alive :) Also, even if it is closed, you can always reopen the PR when you're ready. Thank you for contributing.

[s-aga-r]

One issue with the change (don't send qty back https://github.com/frappe/erpnext/pull/38772/commits/948fd3d689664853c4c41d817ad21de76e0c921f) is we need to set the default value (1) for the qty field in transaction.py and in DocType default value.