kernel_2d_fixed giving false assertion errors

[meshtag]

Actual behavior

boost::gil::detail::kernel_2d_fixed gives false assertion errors during its initialization.

Expected behavior

A 2D kernel with provided values and center co-ordinates should be created

C++ Minimal Working Example

https://wandbox.org/permlink/apUAhyheZUyea3UO

#include <boost/gil.hpp>
namespace gil = boost::gil;
int main
{
    // your code
    std::array<int, 81> v = {0};
    gil::detail::kernel_2d_fixed<int, 9> kernel(v.cbegin(), 4, 4); // Not ok
}

This problem remained unnoticed in CI build due to this macro.

Environment

• Compiler version: gcc 11.1.0
• Version: Boost 1.76.0

[meshtag]

A simple workaround for this problem is here. However, I think this issue can be dealt with in a more reliable/generic manner.