fix: correct index for limit in book_offers CLI

[mvadari]

High Level Overview of Change

This PR fixes an indexing typo in the book_offers CLI processing. This does not affect the HTTPS/WS RPC processing.

It's a fairly straightforward fix - there is a length check on whether the list length is >= 5, but the 5u index is taken instead of the 4u index (as the last in the list).

Context of Change

Reported as a part of the Lending Protocol Attackathon

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (non-breaking change that only restructures code)
• Performance (increase or change in throughput and/or latency)
• Tests (you added tests for code that already exists, or your new feature included in this PR)
• Documentation update
• Chore (no impact to binary, e.g. .gitignore, formatting, dropping support for older tooling)
• Release

API Impact

There is a minor fix in the book_offers CLI. This does not affect the HTTPS/WS RPC processing.

Test Plan

CI passes.

[codecov]

Codecov Report

❌ Patch coverage is 72.72727% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.6%. Comparing base (6ff495f) to head (532c30e).
⚠️ Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/xrpld/rpc/detail/RPCCall.cpp	72.7%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #6043   +/-   ##
=======================================
  Coverage     78.6%   78.6%           
=======================================
  Files          818     818           
  Lines        68983   68989    +6     
  Branches      8246    8241    -5     
=======================================
+ Hits         54196   54210   +14     
+ Misses       14787   14779    -8     

Files with missing lines	Coverage Δ
src/xrpld/rpc/detail/RPCCall.cpp	93.7% <72.7%> (-0.4%)	⬇️

... and 3 files with indirect coverage changes

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[mvadari]

#6044 is a version of this PR that covers more cases and is broader. We may want to merge this first or go straight to that one, unsure.

[bthomee]

@Tapanito are there any additional things that need to be addressed, or is this good to go?

[Tapanito]

@Tapanito are there any additional things that need to be addressed, or is this good to go?

Good to go @bthomee