C type error in the ov_rest plugin

[fweimer-rh]

NULL can have a pointer type, and converting pointers to integers without a cast is not valid C. Compilers are beginning to treat this an error, leading to a build failure.

Related to:

• https://fedoraproject.org/wiki/Changes/PortingToModernC
• https://fedoraproject.org/wiki/Toolchain/PortingToModernC