Don't set *pval to NULL in ASN1_item_ex_new.

While *pval is usually a pointer in rare circumstances it can be a long
value. One some platforms (e.g. WIN64) where
sizeof(long) < sizeof(ASN1_VALUE *) this will write past the field.

*pval is initialised correctly in the rest of ASN1_item_ex_new so setting it
to NULL is unecessary anyway.

Thanks to Julien Kauffmann for reporting this issue.
Reviewed-by: NRichard Levitte <levitte@openssl.org>

crypto/asn1/tasn_new.c

@@ -94,8 +94,6 @@ int ASN1_item_ex_new(ASN1_VALUE **pval, const ASN1_ITEM *it)
     else
         asn1_cb = 0;
 
-    *pval = NULL;
-
 #ifdef CRYPTO_MDEBUG
     if (it->sname)
         CRYPTO_push_info(it->sname);