Fix missing dereference.

Went unnoticed because it was only on a defensive code path, in an internal
function, so not exercised.
diff --git a/library/x509_crt.c b/library/x509_crt.c
index 5f9b74f..25aaff3 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -2182,8 +2182,8 @@
     /* extra precaution against mistakes in the caller */
     if( parent == NULL )
     {
-        parent_is_trusted = 0;
-        signature_is_good = 0;
+        *parent_is_trusted = 0;
+        *signature_is_good = 0;
     }
 
     return( 0 );