Added volatile to offset variable. 

The crash was coming from optimization issues which is solved with volatile.
Possible source of this problem is a -ftrapv compilation flag I have.

Solution for issue:
https://github.com/ros/common_msgs/issues/6

Explanation copied from the above issue:
I've been running experiments with the tabletop_object_detector and found that the segmentation crashed. Those detection/segmentation nodes are passing pointclouds by sensor_msgs::PointCloud, not PointCloud2.
The bug always comes when sensor_msgs::convertPointCloudToPointCloud2() is called. I captured the point clouds that are being pushed to the converter at that time.

I set up a node that reproduces the bug. The code is the following:
http://pastebin.com/j6PUF2G7

Bag file with the data that produces the error: (~10MB)
https://www.dropbox.com/s/4fwc0d7d8vihsq0/points_cut2.bag