Bug 1147730 part 2 - Validate input rather than not-yet-set data field in MediaKeySession::SetSessionId. r=jw_wang

dom/media/eme/CDMProxy.cpp

@@ -396,7 +396,9 @@ CDMProxy::OnSetSessionId(uint32_t aCreateSessionToken,
   }
 
   nsRefPtr<dom::MediaKeySession> session(mKeys->GetPendingSession(aCreateSessionToken));
-  session->SetSessionId(aSessionId);
+  if (session) {
+    session->SetSessionId(aSessionId);
+  }
 }
 
 void

dom/media/eme/MediaKeySession.cpp

@@ -66,7 +66,7 @@ MediaKeySession::MediaKeySession(JSContext* aCx,
 void MediaKeySession::SetSessionId(const nsAString& aSessionId)
 {
   EME_LOG("MediaKeySession[%p,'%s'] session Id set",
-          this, NS_ConvertUTF16toUTF8(mSessionId).get());
+          this, NS_ConvertUTF16toUTF8(aSessionId).get());
 
   if (NS_WARN_IF(!mSessionId.IsEmpty())) {
     return;