Init variables, check for valid file pointers before using, provide valid return values

[lazydroid]

This MR fixes minor issues in the using uninitialized variables, returning nollptr instead of std::string, using file pointers without checking them for validity and similar things. This is not a complete list of issues, but the most dangerously looking ones.

[rdiankov]

Can you have Puttichai look at the changes related to planning? Thanks

[lazydroid]

There's a conditional passing of NULL pointer with null pointer dereference, do you have any idea why do we need to convert vectors to raw pointers instead of just iterating over the vectors with the approximately same result?

[lazydroid]

Looks good to me now.

Thank you!

[rdiankov]

thanks~