Fix for chainIndex out of bounds in BillboardChain::addChainElement

[bponsler]

Fixing a bug in the BillboardLine class when setting up the chains. The case where the number of points is an exact multiple of 16384 (MAX_ELEMENTS) was not being handled and resulted in the number of chains being set to 0 which results in ogre throwing the following exception:

terminate called after throwing an instance of 'Ogre::ItemIdentityException'
  what():  OGRE EXCEPTION(5:ItemIdentityException): chainIndex out of bounds in BillboardChain::addChainElement at /build/buildd/ogre-1.8-1.8.1+dfsg/OgreMain/src/OgreBillboardChain.cpp (line 243)

This issue has been mentioned in: ORB_SLAM issue 60, ORB_SLAM issue 21, hratc2015_framework issue 4, and here

This issue is easy to reproduce using the following steps:

1. Open rviz
2. Set the fixed frame to "map"
3. Add a "Marker" display to rviz
4. Make sure the marker is subscribed to "visualization_marker" topic (this should be the default)
5. Publish a Marker with an exact multiple of 16384 points in it
6. rviz will crash due to chainIndex out of bounds (see the script in test-break-rviz.zip)

[gitunit]

@wjwwood looks like a fix, what do you think, can we expect that included someday?

[wjwwood]

lgtm. I was able to reproduce it and see that this change fixes the crash. I also had a look at some examples that used chains to make sure there weren't any obvious breaks to normal usage.

Thanks, and sorry for the delay in getting it merged.

[gitunit]

cool. thank you both