fix: don't fetch item_code if already exists.

[dj12djdjs]

The problem is if you're processing a return where an old barcode no longer exists in the item master. You'll get an error Barcode for item X not found.

The solution, if the item_code already exists, no need to fetch it.

[ankush]

Ah, I came across this just recently!

[codecov]

Codecov Report

Merging #31113 (4f8172c) into develop (1ecb8f4) will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop   #31113      +/-   ##
===========================================
+ Coverage    63.14%   63.19%   +0.05%     
===========================================
  Files          986      986              
  Lines        67361    67361              
===========================================
+ Hits         42535    42569      +34     
+ Misses       24826    24792      -34     

Impacted Files	Coverage Δ
erpnext/stock/get_item_details.py	80.44% <100.00%> (ø)
...tch_item_expiry_status/batch_item_expiry_status.py	67.92% <0.00%> (-24.53%)	⬇️
...wise_balance_history/batch_wise_balance_history.py	67.79% <0.00%> (-22.04%)	⬇️
erpnext/hr/doctype/job_offer/job_offer.py	82.92% <0.00%> (-4.88%)	⬇️
.../fifo_queue_vs_qty_after_transaction_comparison.py	93.10% <0.00%> (-1.73%)	⬇️
erpnext/crm/doctype/prospect/prospect.py	56.71% <0.00%> (-1.50%)	⬇️
...ype/account/chart_of_accounts/chart_of_accounts.py	76.87% <0.00%> (-0.69%)	⬇️
erpnext/stock/doctype/batch/batch.py	82.80% <0.00%> (-0.64%)	⬇️
...t/accounts/report/sales_register/sales_register.py	70.76% <0.00%> (-0.59%)	⬇️
erpnext/selling/doctype/quotation/quotation.py	52.04% <0.00%> (-0.52%)	⬇️
... and 29 more