fix: use base_net_amount in case of missing stock qty

[ruthra-kumar]

Item-wise Purchase Register will include debit notes with stock qty as '0'.

[codecov[bot]]

Codecov Report

Merging #33457 (506ca39) into develop (4076999) will decrease coverage by 0.01%. The diff coverage is n/a.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #33457      +/-   ##
===========================================
- Coverage    64.10%   64.08%   -0.02%     
===========================================
  Files          818      818              
  Lines        58670    58713      +43     
===========================================
+ Hits         37609    37625      +16     
- Misses       21061    21088      +27     

Impacted Files	Coverage Δ
...e_purchase_register/item_wise_purchase_register.py	58.58% <ø> (+1.16%)	:arrow_up:
erpnext/selling/doctype/sales_order/sales_order.py	80.10% <0.00%> (-0.18%)	:arrow_down:
...customer_ledger_summary/customer_ledger_summary.py	0.00% <0.00%> (ø)
...xt/accounts/doctype/payment_entry/payment_entry.py	72.58% <0.00%> (+0.03%)	:arrow_up:
...ccounts/doctype/payment_request/payment_request.py	68.09% <0.00%> (+0.07%)	:arrow_up: