[boost] [graph] r_c_shortest_paths writes/reads outside allocated memory

Dear Colleagues, The algorithm for computing resource constrained shortest path writes/reads outside allocated memory which may result in segmentation faults. The finding is confirmed using Valgrind. I fixed the bug and opened a pull request. Could you review the pull request and give feedback if there is something more that should be done to meet quality requirements for the merge? The pull request https://github.com/boostorg/graph/pull/93 explains the issue, fixes it and contains a test for preventing regressions. Thank you in advance for your help. Regards, Mateusz Polnik