FINERACT-2432: Avoid NPE when loanScheduleType is null/invalid

[siva-sai-udaygiri]

Fix NPE/IllegalArgumentException in LoanProductDataValidator when loanScheduleType is null/blank/invalid.

Instead of calling LoanScheduleType.valueOf(...) directly, this adds a guard + safe parsing and then reuses the parsed enum for the remaining checks.

Tested: ./gradlew :fineract-provider:resolve (local)

[siva-sai-udaygiri]

@adamsaghy I recreated the PR from a clean branch and the conflicts are gone now. Could you please take another look when you have a moment?

[siva-sai-udaygiri]

@adamsaghy Spotless formatting is fixed on the latest commit.

CI is still failing in test (test-core-4). The failure happens during test cleanup (LoanTestLifecycleExtension.afterEach) when the integration test calls:GET /fineract-provider/api/v1/internal/loan/status/100 and receives HTTP 500.

Stacktrace points here: org.apache.fineract.integrationtests.common.loans.LoanTransactionHelper.getLoanIdsByStatusId(LoanTransactionHelper.java:3102)

My PR only changes LoanProductDataValidator (loanScheduleType null/invalid guard) and doesn’t touch COB/internal loan status endpoints. Could you please advise if this is a known flaky/infra issue and/or re-run the test-core-4 job?