Check $S/backend/impress/zip.{c,h}.
after reviewing headers, it appears this is in fact a false positive. For example, in evince: zip *zip_open (const char *fname, int *err); void zip_close (zip *z); char *zip_error (int err); int zip_load (zip *z, const char *name, char *buf); and in libzip: ZIP_EXTERN struct zip *zip_open(const char *, int, int *); ZIP_EXTERN int zip_close(struct zip *); no zip_load and zip_error in zip.h so all considered it can't be the same.