free NULL cleanup

Start ensuring all OpenSSL "free" routines allow NULL, and remove
any if check before calling them.
This gets DH_free, DSA_free, RSA_free

Reviewed-by: Matt Caswell <matt@openssl.org>

engines/e_chil.c

@@ -849,8 +849,7 @@ static EVP_PKEY *hwcrhk_load_privkey(ENGINE *eng, const char *key_id,
     return res;
  err:
 #  ifndef OPENSSL_NO_RSA
-    if (rtmp)
-        RSA_free(rtmp);
+    RSA_free(rtmp);
 #  endif
     return NULL;
 }