al_set_path_extension - Allegro 5 API
bool al_set_path_extension(ALLEGRO_PATH *path, char const *extension)
Replaces the extension of the path with the given one, i.e. replaces
everything from the final dot (`.') character onwards, including the dot. If
the filename of the path has no extension, the given one is appended. Usually
the new extension you supply should include a leading dot.
Returns false if the path contains no filename part,
i.e. the filename part is the empty string.