Feature/assert fix

[khancyr]

In file included from ../../libraries/AP_Math/control.h:4,
                 from ../../libraries/AC_WPNav/AC_WPNav_OA.cpp:1:
../../libraries/AP_Math/vector2.h: In member function ‘T& Vector2<T>::operator[](uint8_t)’:
../../libraries/AP_Math/vector2.h:123:9: error: there are no arguments to ‘assert’ that depend on a template parameter, so a declaration of ‘assert’ must be available [-fpermissive]
  123 |         assert(i >= 0 && i < 2);
      |         ^~~~~~
compilation terminated due to -Wfatal-errors.

when building copter with waf configure --enable-math-check-indexes