Wrong 2d joint possitions

[Angel Noe Martinez]

Dear @mohomran,

Thank you very much for your great contribution and code for experimentation.
The demo works fine and I was able to visualize the mesh with --visualise render option.
However, with --visualise pose the output only produce a black image with no displayed
joints in the 2d plane.

I dug a little bit in the code and found that the output of the get_smpl_joint_locations
function produce very large and some negative numbers for the 2d points.
It might be an issue about the camera matrix used for projection.
I wonder if you can point me out in the good direction on how to fix this issue.