Use nullptr in more places

(This is a merge of http://go/wvgerrit/139630.)

This patch fixes a few places that were using NULL or 0 instead of
nullptr.

Bug: 207702482
Test: x86-64 build
Change-Id: I10e19febebd093fe4445208a082216002d9a4482

libwvdrmengine/cdm/core/src/privacy_crypto_boringssl.cpp

@@ -324,7 +324,7 @@ bool ExtractExtensionValueFromCertificate(const std::string& cert,
       reinterpret_cast<const unsigned char*>(cert.data());
   long cert_size = static_cast<long>(cert.size());
   boringssl_ptr<PKCS7, PKCS7_free> pkcs7(
-      d2i_PKCS7(NULL, &cert_data, cert_size));
+      d2i_PKCS7(nullptr, &cert_data, cert_size));
   if (!pkcs7) {
     LOGE("Error parsing PKCS7 message");
     return false;