Fix errors being hidden by Protobuf warning-disabling

(This is a merge of http://go/wvgerrit/140850.)

This patch fixes a number of minor issues in the codebase (mostly
instances of 0-as-nullptr, but also some member shadowing and a missing
override) that were being hidden by the fact that depending on Protobuf
disables these diagnostics. And which will be unhidden when a later
patch removes that behavior from Protobuf.

Bug: 208304830
Test: x86-64
Change-Id: I4b0b1264748880b3726a6388d589868d898f949e

libwvdrmengine/cdm/core/test/license_unittest.cpp

@@ -535,9 +535,12 @@ TEST_F(CdmLicenseTest, PrepareKeyRequestValidationV15) {
 }
 
 struct EntitledKeyVariant {
-  EntitledKeyVariant(const char* name, const std::string& key,
-                     bool should_succeed)
-      : name(name), key(key), should_succeed(should_succeed) {}
+  EntitledKeyVariant(const char* name_param, const std::string& key_param,
+                     bool should_succeed_param)
+      : name(name_param),
+        key(key_param),
+        should_succeed(should_succeed_param) {}
+
   const std::string name;
   const std::string key;
   const bool should_succeed;