Added a reproducible example for Illegal index c++ error

[byapparov]

This is an error investigation request, not intended for merge.

To see the symptoms on Mac:

• Execute tests/testthat/test-bad-index.R
• In sol vector you will notice large non-integer values, e.g. 5e24

To see symptoms on Debian:

• install Docker: https://docs.docker.com/docker-for-mac/install/
• navigate to the project folder and execute in terminal: docker build -t rcbc:1.0 .
• once container is built run the container: run -t -i --rm rcbc:1.0 bash
• in docker shell cd code ; Rscript test-bad-index.R

You should see error:

Illegal index 633 in OsiClpSolverInterface::setInteger Error in cpp_cbc_solve(obj = obj, isMaximization = max, rowIndices = mat@i, : c++ exception (unknown reason) Calls: cbc_solve -> cpp_cbc_solve -> .Call Execution halted

UPD: I think I have managed to solve the issue by setting volume to very small values 1e-10 where it is zero.