message: backend: fix for ERROR define on Windows
diff: #include "plugins/offboard/offboard.h"
  #include "offboard/offboard_service_impl.h"
  +// On Windows the build fails if a define for ERROR is leaked after
  +// above includes.
  +//
  +// The compile error is:
  +// "illegal token on right side of '::'"
  +// in Camera::Result::ERROR.
  +#ifdef ERROR
  +#undef ERROR
  +#endif
  +
  namespace mavsdk {
  namespace backend {
  