operator new doesn't return null anyway

(and assigning nullptr to a null xcert was apparently redundant)

Change-Id: I8b6120248c042adcb2f787b8db0f28c14268212d
Reviewed-on: https://gerrit.libreoffice.org/73019
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

xmlsecurity/source/xmlsec/nss/securityenvironment_nssimpl.cxx

@@ -797,11 +797,7 @@ X509Certificate_NssImpl* NssCertToXCert( CERTCertificate* cert )
 
     if( cert != nullptr ) {
         xcert = new X509Certificate_NssImpl() ;
-        if( xcert == nullptr ) {
-            xcert = nullptr ;
-        } else {
-            xcert->setCert( cert ) ;
-        }
+        xcert->setCert( cert ) ;
     } else {
         xcert = nullptr ;
     }