Fix clang compiler errors

Fix clang compiler errors

Fixes following errors as reported by clang compilers:

 cgi-io/src/main.c:723:12: error: unused variable 'post' [-Werror,-Wunused-variable]
         autochar *post = postdecode(fields, 4);
                  ^
 cgi-io/src/main.c:814:12: error: unused variable 'post' [-Werror,-Wunused-variable]
         autochar *post = postdecode(fields, 1);
                  ^
 cgi-io/src/main.c:996:12: error: unused variable 'post' [-Werror,-Wunused-variable]
         autochar *post = postdecode(fields, 4);

Signed-off-by: Petr Štetiar <[email protected]>