Work around warning-as-error on some compilers
On GCC 9.4 fix this error: error: parameter ‘callback’ set but not used [-Werror=unused-but-set-parameter]
Fixes #6 (closed)
On GCC 9.4 fix this error: error: parameter ‘callback’ set but not used [-Werror=unused-but-set-parameter]
Fixes #6 (closed)