fix: fix the issue where sending assets using TransactionBuilder.buildPaymentToContractTransaction fails when the sender's account is the same as the asset issuer's account.

[overcat]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.18%. Comparing base (493816c) to head (7b2b736).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #685   +/-   ##
=========================================
  Coverage     80.18%   80.18%           
- Complexity     1226     1227    +1     
=========================================
  Files           213      213           
  Lines          4820     4820           
  Branches        411      412    +1     
=========================================
  Hits           3865     3865           
  Misses          703      703           
  Partials        252      252           

Files with missing lines	Coverage Δ
.../main/java/org/stellar/sdk/TransactionBuilder.java	95.28% <100.00%> (ø)

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.