civetweb.c: fix potential memory leak in set_ports_options

Free 'ptr' in case realloc was successful, but the next check fails.

Fix for clang scan-build report:

5886 if (!success) {

    35 Potential leak of memory pointed to by 'ptr'

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>