small heif-enc bug

[pcdion]

in examples/heif_enc.cc ln 779, there's this line : std::string input_filename = tile_generator.filename(0, 0);

yields a build error with C++20: error: conversion from 'std::filesystem::__cxx11::path' to non-scalar type 'std::string' {aka 'std::__cxx11::basic_string<char>'} requested1

Issue resolved using the filesystem string() method: std::string input_filename = tile_generator.filename(0, 0).string();

@farindk

[bradh]

@pcdion You know you can do PR, right?

[pcdion]

#1400