Fix GH-23418: UAF when accessing mounted Phar subdirectories

[LamentXU123]

The UAF is basically because we trick the phar_mount_entry to fail and the code goes to

if (SUCCESS != phar_mount_entry(phar, test, test_len, path, path_len)) {
	efree(test);
	if (error) {
		spprintf(error, 4096, "phar error: path \"%s\" exists as file \"%s\" and could not be mounted", path, test);
		}

Self-evident buggy code I'd say... we freed test and use it in spprintf. And guess what, the whole function repeats this insane logic later again. So this is fixing two potential UAFs.

Here we passes a properly null-terminated copy of the shortened path to phar_mount_entry() instead and keep test alive until error formatting and manifest lookup have completed.