Wrong error message

[HannesVanOverloop]

https://github.com/humanoid-path-planner/hpp-pinocchio/blob/bcd11eb78aad30a94a6bea25a3161caac7c0f3ba/src/urdf/util.cc#LL448C43-L448C43
If the file passed as an argument to loadModel does not exist, we get the following error message "Failed to parse URDF. Use check_urdf command to know what's wrong."
It might be useful to check the existence of the file before calling ::urdf::parseURDFFile.