wget cookies.c PREPEND_SLASH macro uses strcpy into alloca'd buffer without input length caps

In GNU Wget's cookies handling, the PREPEND_SLASH macro creates a stack buffer with alloca based on strlen(s) and then uses strcpy into it without enforcing an upper bound on the length of s. When s is attacker-controlled via the PATH component passed to cookie_handle_set_cookie, this can trigger stack exhaustion/DoS from massive alloca and can cause memory corruption if strlen/pointer assumptions are violated.