Segfault from Linkage::Criteria::expandToTarget()

[jslee02]

Linkage.cpp Ln:364

  // If we have successfully reached the target, expand from there
  if(newBns.back() == _target.mNode.lock())
    expansionPolicy(_target.mNode.lock(), _target.mPolicy, newBns);

Segfault is raised at newBns.back() when newBns is empty. According to cppreference, calling back on an empty container is undefined. I observed that this segfault is happened on Windows but not Ubuntu or Mac.

[mxgrey]

This is actually a really easy fix. This is just an unhandled edge case where the linkage wasn't able to expand towards the target whatsoever. The current code incorrectly assumes that it was able to take at least one step towards the target. We just need to change the if-statement to if(newBns.size() > 0 && newBns.back() == _target.mNode.lock()). I'll make a pull request with the fix.

[jslee02]

Thanks! I confirmed that it fixes the segfault. I just made a comment on #490 about minor code preference.

[jslee02]

Fixed by #490, #491, and #492.