The following functions return immediately if a null pointer was passed.
* asn1p_constraint_free
* asn1p_paramlist_free
* asn1p_ref_free
* asn1p_value_free
* asn1p_wsyntx_free

It is therefore not needed that a function caller repeats a corresponding check.

This issue was fixed by using the software "Coccinelle 1.0.4".
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>