fix: autoreload when directory is root (#498)

for cases like "/file", `base - filepath` will result in 0
instead of 1.

regression introduced in: 94d531fd82

Reviewed-on: https://codeberg.org/nsxiv/nsxiv/pulls/498
Reviewed-by: eylles <eylles@noreply.codeberg.org>

autoreload.c

@@ -86,7 +86,7 @@ void arl_add(arl_t *arl, const char *filepath)
 
 	base = strrchr(filepath, '/');
 	assert(base != NULL); /* filepath must be result of `realpath(3)` */
-	dir = arl_scratch_push(filepath, base - filepath);
+	dir = arl_scratch_push(filepath, MAX(base - filepath, 1));
 	add_watch(arl->fd, &arl->wd_dir, dir, IN_CREATE | IN_MOVED_TO);
 	arl->filename = arl_scratch_push(base + 1, strlen(base + 1));
 }