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/oemcrypto/test/oec_session_util.h

@@ -602,7 +602,7 @@ class Session {
   // order to verify signatures.
   void GenerateReport(const std::string& pst,
                       OEMCryptoResult expected_result = OEMCrypto_SUCCESS,
-                      Session* other = 0);
+                      Session* other = nullptr);
   // Move this usage entry to a new index.
   void MoveUsageEntry(uint32_t new_index, std::vector<uint8_t>* header_buffer,
                       OEMCryptoResult expect_result = OEMCrypto_SUCCESS);