fix: typeerror on invoice creation from SO/PO

[ruthra-kumar]

Issue

"TypeError: unsupported operand type(s) for *: 'NoneType' and 'float'" occurs when an invoice is created from SO/PO.

Replication Steps

'Automatically Fetch Payment Terms from Order' is enabled.

SO/PO should have payment term with '0%' invoice portion.

Create-> Sales/Purchase Invoice should throw error

Fix

The payment_schedule object created by auto fetch feature has uninitialised attribute 'payment_amount' which causes this error. It has been fixed in this change.

[codecov]

Codecov Report

Merging #29560 (0f913e0) into develop (8eff296) will increase coverage by 5.41%.
The diff coverage is 50.00%.

@@             Coverage Diff             @@
##           develop   #29560      +/-   ##
===========================================
+ Coverage    53.59%   59.00%   +5.41%     
===========================================
  Files         1111     1112       +1     
  Lines        69328    69469     +141     
===========================================
+ Hits         37153    40989    +3836     
+ Misses       32175    28480    -3695     

Impacted Files	Coverage Δ
erpnext/controllers/accounts_controller.py	84.51% <50.00%> (+3.78%)	⬆️
...t/payroll/doctype/payroll_period/payroll_period.py	64.81% <0.00%> (-5.56%)	⬇️
.../report/bom_operations_time/bom_operations_time.py	89.13% <0.00%> (-2.18%)	⬇️
erpnext/stock/report/stock_ledger/stock_ledger.py	84.55% <0.00%> (-0.82%)	⬇️
...ype/account/chart_of_accounts/chart_of_accounts.py	77.39% <0.00%> (-0.69%)	⬇️
erpnext/accounts/report/financial_statements.py	35.24% <0.00%> (-0.39%)	⬇️
erpnext/projects/doctype/project/project.py	54.54% <0.00%> (ø)
erpnext/payroll/doctype/salary_slip/salary_slip.py	83.89% <0.00%> (ø)
.../report/stock_projected_qty/stock_projected_qty.py	88.15% <0.00%> (ø)
erpnext/e_commerce/product_data_engine/query.py	75.53% <0.00%> (ø)
... and 165 more