Enforce valid range of LoanSet.InterestRate

- Addresses FIND-002 from audit.
- Enforces a range of 0-100% in 1/10 bips.
- Also add a couple of unit test checks.

src/test/app/Loan_test.cpp

@@ -748,6 +748,19 @@ class Loan_test : public beast::unit_test::suite
             loanSetFee,
             ter(temINVALID));
 
+        // sfInterestRate: good value, bad account
+        env(set(evan, broker.brokerID, principalRequest, startDate),
+            sig(sfCounterpartySignature, borrower),
+            interestRate(maxInterestRate),
+            loanSetFee,
+            ter(tefBAD_AUTH));
+        // sfInterestRate: too big
+        env(set(evan, broker.brokerID, principalRequest, startDate),
+            sig(sfCounterpartySignature, lender),
+            interestRate(maxInterestRate + 1),
+            loanSetFee,
+            ter(temINVALID));
+
         // sfLateInterestRate: good value, bad account
         env(set(evan, broker.brokerID, principalRequest, startDate),
             sig(sfCounterpartySignature, borrower),

src/xrpld/app/tx/detail/LoanSet.cpp

@@ -82,6 +82,8 @@ LoanSet::preflight(PreflightContext const& ctx)
     if (auto const data = tx[~sfData]; data && !data->empty() &&
         !validDataLength(tx[~sfData], maxDataPayloadLength))
         return temINVALID;
+    if (!validNumericRange(tx[~sfInterestRate], maxInterestRate))
+        return temINVALID;
     if (!validNumericRange(tx[~sfOverpaymentFee], maxOverpaymentFee))
         return temINVALID;
     if (!validNumericRange(tx[~sfLateInterestRate], maxLateInterestRate))